#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;

typedef long long ll;
//面向对象学习
class Person {
public:
    ll a, b;
    Person(ll i, ll j) : a(i), b(j) {}
    Person() {}
    friend bool operator<(const Person &A, const Person &B) { return (B.a * A.b < A.a * B.b); }
};

const int maxn = 1e5 + 5;
Person person[maxn];

/* 解决思想:
贪心的思想：题目的特点
1.总共等待的时间是一定的
2.贪心的直觉是先排ai/bi大的即单位等待时间内暴躁值更大的在前面
3.通过JM的介绍可以用相邻交换法证明其正确性
 */

int main() {
    int n, a, b;
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        scanf("%lld%lld", &person[i].a, &person[i].b);
    }
    // sort
    sort(person + 1, person + 1 + n);
    //
    ll minSum = 0, time = 0;
    for (int i = 1; i <= n; i++) {
        time += person[i].b;
        minSum += person[i].a * time;
    }
    //
    printf("%lld\n", minSum);
    return 0;
}