#include <bits/stdc++.h>   using namespace std;   const int N = 100010;   pair<int, int> a[N];   int s[N], ss[N];   int main() {     int n, m;     scanf( %d , &n);     for (int i = 0; i < n; i++) {       scanf( %d%d , &ss[i], &a[i].first);       a[i].second = i;     }     s[n - 1] = ss[n - 1];     for (int i = n - 2; i >= 0; i--) s[i] = ss[i] + s[i + 1];     sort(a, a + n);     int now = n, ans = 0;     for (int i = 0; i < n; i++) {       if (a[i].second < now) {         ans += (a[i].first * (s[a[i].second] - s[now]));         now = a[i].second;       }     }     printf( %d n , ans);     return 0;   }   