#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
typedef long long ll;

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 MAX = 1e5 + 5;
Person persons[MAX];

int main() {
    // freopen("test.txt", "r", stdin);
    int n;
    while (scanf("%d", &n) != EOF) {
        // 输入
        for (int i = 1; i <= n; i++) {
            scanf("%lld %lld", &persons[i].a, &persons[i].b);
        }
        // 排序
        sort(persons + 1, persons + 1 + n);
        // 求解
        ll res = 0;
        ll sum = 0;
        for (int i = 1; i <= n; i++) {
            sum += persons[i].b;
            res += persons[i].a * sum;
        }
        // 输出
        printf("%lld\n", res);
    }
    return 0;
}