#include <iostream>

 #include <cstdio>

 #include <algorithm>

 using namespace std;

 struct node

 {

     int t, d;

 };

 int n;

 node a[];

 int sum[];

 bool cmp(const node & a, const node & b)

 {

     double x = a.d * 1.0 / a.t;

     double y = b.d * 1.0 / b.t;

     return x > y;

 }

 int main()

 {

     cin >> n;

     for (int i = ; i < n; i++)

     {

         scanf("%d %d", &a[i].t, &a[i].d);

     }

     sort(a, a + n, cmp);

     sum[n - ] = a[n - ].d;

     for (int i = n - ; i >= ; i--)

     {

         sum[i] = sum[i + ] + a[i].d;

     }

     long long total = ;

     for (int i = ; i < n - ; i++)

     {

         total += sum[i + ] *  * a[i].t;

     }

     cout << total << endl;

     return ;

 }