#define _CAT_SECURE_NO_WARNINGS
#include <stdio.h>

long long int zhizhen1 = 0;  //设置指针1
long long int sum = 0;       //用以记录已经处理过的牌数
long long int he = 0;        //设置cyy的和

long long int str1[100000] = { 0 }, str2[100000] = { 0 }, str3[100000] = { 0 }, str4[100000] = { 0 },
              str5[100000] = { 0 };  //全局变量-可在子函数和主函数中应用

void shuru(long long int n);                                    //输入函数
void paixv(long long int n);                                    //排序函数
void shenrupaixv(long long int n);                              //深入排序函数
void yanzheng(long long int n);                                 //验证函数
void bianma(long long int n);                                   //编码函数
void bianmacsf(long long int n);                                // csf的编码函数
void paixvcsf(long long int n);                                 // csf的排序函数
void shenrupaixvcsf(long long int n);                           // csf的深入排序函数
long long int xunzuizhi(long long int n);                       //用以寻找str1中的最大值
long long int qinglingcsf(long long int n, long long int max);  // csf的清零函数
void qushu(long long int n, long long int zhizhen1);  //取数函数，用于取出str2中的两个可取数

void case1(long long int zhizhen6, long long int zhizhen8);  //情况1处理函数，一大一小牌。
void case2(long long int zhizhen6, long long int zhizhen8);  //两张大牌的函数
void case3(long long int zhizhen6, long long int zhizhen8, long long int n,
           long long int paishu);  //两张小牌的处理函数

void case3(long long int zhizhen6, long long int zhizhen8, long long int n, long long int paishu) {
    for (long long int l = zhizhen8; l < n; l++) {
        if (str3[l] <= paishu) {
            he = he + str2[l];
            str1[l] = str2[l] = 0;
            sum++;
            break;
        }
    }
}

void case2(long long int zhizhen6, long long int zhizhen8) {
    if (str2[zhizhen6] > str2[zhizhen8]) {
        he = he + str2[zhizhen6];
        str1[zhizhen6] = str2[zhizhen6] = 0;
        sum++;
    } else if (str2[zhizhen6] < str2[zhizhen8]) {
        he = he + str2[zhizhen8];
        str1[zhizhen8] = str2[zhizhen8] = 0;
        sum++;
    } else if (str2[zhizhen6] == str2[zhizhen8]) {
        if (str1[zhizhen6] >= str1[zhizhen8]) {
            he = he + str2[zhizhen6];
            str1[zhizhen6] = str2[zhizhen6] = 0;
            sum++;
        } else {
            he = he + str2[zhizhen8];
            str1[zhizhen8] = str2[zhizhen8] = 0;
            sum++;
        }
    }
}

void bianmacsf(long long int n) {
    for (long long int i = 0; i < n; i++) {
        str5[i] = i + 1;
    }  //用str5对数组1从大到小进行编号
}

void case1(long long int zhizhen6, long long int zhizhen8) {
    if (str2[zhizhen6] > str2[zhizhen8]) {
        he = he + str2[zhizhen6];
        str1[zhizhen6] = str2[zhizhen6] = 0;
        sum++;
    } else if (str2[zhizhen6] < str2[zhizhen8]) {
        he = he + str2[zhizhen8];
        str1[zhizhen8] = str2[zhizhen8] = 0;
        sum++;
    } else if (str2[zhizhen6] == str2[zhizhen8]) {
        if (str1[zhizhen6] >= str1[zhizhen8]) {
            he = he + str2[zhizhen6];
            str1[zhizhen6] = str2[zhizhen6] = 0;
            sum++;
        } else {
            he = he + str2[zhizhen8];
            str1[zhizhen8] = str2[zhizhen8] = 0;
            sum++;
        }
    }
}

void qushu(long long int n, long long int zhizhen1) {
    long long int j = 0;  //用以记录str4的个数

    for (long long int k = zhizhen1; k < n; k++) {
        if (str2[k] != 0) {
            str4[j] = str3[k];
            j++;
            str4[j] = str5[k];
            j++;
            if (j >= 4)
                break;
        }
    }  //取出str2中的两位
}

long long int qinglingcsf(long long int n, long long int max) {
    for (long long int i = 0; i < n; i++) {
        if (str1[i] == max) {
            str1[i] = str2[i] = 0;
            zhizhen1 = i;
            sum++;
            break;
        }
    }
    return zhizhen1;
}

long long int xunzuizhi(long long int n) {
    long long int max = str1[0];
    for (long long int i = 1; i <= n; i++) {
        if (str1[i] > max) {
            max = str1[i];
        }
    }  //用以找到str1中的最大点
    return max;
}

void shenrupaixvcsf(long long int n) {
    for (long long int i = 0; i < n; i++) {
        long long int geshu = 0;
        long long int zhizhen;
        while (str1[i] == str1[i + 1]) {
            geshu = 2;
            zhizhen = i;
            for (long long int j = i + 1; j < n; j++) {
                if (str1[j] == str1[j + 1]) {
                    geshu++;
                } else
                    break;
            }

            if (geshu == 2) {
                if (str2[i] < str2[i + 1]) {
                    long long int temp1 = str1[i + 1];
                    str1[i + 1] = str1[i];
                    str1[i] = temp1;

                    long long int temp2 = str2[i + 1];
                    str2[i + 1] = str2[i];
                    str2[i] = temp2;

                    long long int temp3 = str3[i + 1];
                    str3[i + 1] = str3[i];
                    str3[i] = temp3;
                }
            } else if (geshu > 2) {
                for (long long int i = zhizhen; i < (zhizhen + geshu); i++) {
                    for (long long int j = (zhizhen + geshu - 1); j > i; j--) {
                        if (str1[j] > str1[j - 1]) {
                            long long int temp1 = str1[j];
                            str1[j] = str1[j - 1];
                            str1[j - 1] = temp1;

                            long long int temp2 = str2[j];
                            str2[j] = str2[j - 1];
                            str2[j - 1] = temp2;

                            long long int temp3 = str3[j];
                            str3[j] = str3[j - 1];
                            str3[j - 1] = temp3;
                        }
                    }
                }  //对整体的牌进行的内部的排序
            }
            i = i + geshu;
        }
    }
}

void paixvcsf(long long int n) {
    for (long long int i = 0; i < n; i++) {
        for (long long int j = n - 1; j > i; j--) {
            if (str1[j] > str1[j - 1]) {
                long long int temp1 = str1[j];
                str1[j] = str1[j - 1];
                str1[j - 1] = temp1;

                long long int temp2 = str2[j];
                str2[j] = str2[j - 1];
                str2[j - 1] = temp2;

                long long int temp3 = str3[j];
                str3[j] = str3[j - 1];
                str3[j - 1] = temp3;
            }
        }
    }  //对csf的牌从大到小进行排序,并联动数组1、2、3进行排序
}

void xiufu(long long int bug);  //修复未知电脑bug函数

void xiufu(long long int bug) {
    if (bug == 0)
        str2[0] = str2[1];
}

void bianma(long long int n) {
    for (long long int i = 0; i < n; i++) {
        str3[i] = i + 1;
    }  //用str3对数组二从大到小进行编号
}

void shenrupaixv(long long int n) {
    for (long long int i = 0; i < n; i++) {
        long long int geshu = 0;
        long long int zhizhen;
        while (str2[i] == str2[i + 1]) {
            geshu = 2;
            zhizhen = i;
            for (long long int j = i + 1; j < n; j++) {
                if (str2[j] == str2[j + 1]) {
                    geshu++;
                } else
                    break;
            }

            if (geshu == 2) {
                if (str1[i] < str1[i + 1]) {
                    long long int temp1 = str1[i + 1];
                    str1[i + 1] = str1[i];
                    str1[i] = temp1;

                    long long int temp2 = str2[i + 1];
                    str2[i + 1] = str2[i];
                    str2[i] = temp2;
                }
            } else if (geshu > 2) {
                for (long long int k = zhizhen; k < (zhizhen + geshu); k++) {
                    for (long long int l = (zhizhen + geshu - 1); l > i; l--) {
                        if (str1[l] > str1[l - 1]) {
                            long long int temp1 = str1[l];
                            str1[l] = str1[l - 1];
                            str1[l - 1] = temp1;

                            long long int temp2 = str2[l];
                            str2[l] = str2[l - 1];
                            str2[l - 1] = temp2;
                        }
                    }
                }  //对整体的牌进行的内部的排序
            }
            i = i + geshu;
        }
    }
}

void paixv(long long int n) {
    for (long long int i = 0; i < n; i++) {
        for (long long int j = n - 1; j > i; j--) {
            if (str2[j] > str2[j - 1]) {
                long long int temp1 = str1[j];
                str1[j] = str1[j - 1];
                str1[j - 1] = temp1;

                long long int temp2 = str2[j];
                str2[j] = str2[j - 1];
                str2[j - 1] = temp2;
            }
        }
    }  //对cyy的牌从大到小进行排序
}

void yanzheng(long long int n) {
    for (long long int i = 0; i < n; i++) {
        printf("%lld %lld\n", str1[i], str2[i]);
    }
}

void shuru(long long int n) {
    for (long long int i = 0; i < n; i++) {
        scanf("%lld", &str1[i]);
        scanf("%lld", &str2[i]);
    }  //输入每张牌的a，b点数
}

int main() {
    long long int n;
    scanf("%lld", &n);             //总牌数
    long long int paishu = n / 2;  //记录cyy要取的总牌数

    shuru(n);  //使用输入函数

    paixv(n);  //使用排序函数

    shenrupaixv(n);  //使用深入排序函数

    bianma(n);  //使用编码函数

    xiufu(str2[0]);  //使用修复电脑未知BUG函数

    paixvcsf(n);  //使用scf的排序函数

    shenrupaixvcsf(n);  //使用csf的深入排序函数

    bianmacsf(n);  //使用csf的编码函数

    //
    while (sum <= n) {
        long long int max = xunzuizhi(n);  //使用寻最值函数-寻找str1中最大的值

        zhizhen1 = qinglingcsf(n, max);  //使用csf的清零函数

        if (str3[zhizhen1] <= paishu)
            paishu++;  //可取牌数大小的动态改变

        qushu(n, zhizhen1);  //使用取数函数

        long long int zhizhen6 = str4[0];
        long long int zhizhen7 = str4[1] - 1;
        long long int zhizhen8 = str4[2];
        long long int zhizhen9 = str4[3] - 1;  // 6,8记录的是str2的序数；7，9记录的是str1的序数

        if ((zhizhen6 <= paishu && zhizhen8 > paishu) || (zhizhen6 > paishu && zhizhen8 <= paishu)) {
            case1(zhizhen7, zhizhen9);  //使用一大一小牌处理函数
        } else if (zhizhen6 <= paishu && zhizhen8 <= paishu) {
            case2(zhizhen7, zhizhen9);  //使用两个大牌函数
        } else if (zhizhen6 > paishu && zhizhen8 > paishu) {
            case3(zhizhen7, zhizhen9, n, paishu);  //使用两张小牌的处理函数
        }
    }

    printf("%lld\n", he);

    return 0;
}