#include <bits/stdc++.h>   using namespace std;   int main() {     int n, a[100000], p[100000];     cin >> n;     for (int i = 0; i < n; ++i) cin >> a[i] >> p[i];     for (int i = 1; i < n; ++i) p[i] = min(p[i], p[i - 1]);     int ans = 0;     for (int i = 0; i < n; ++i) ans += p[i] * a[i];     cout << ans << endl;   }   