#include <bits/stdc++.h>   int main() {     int n;     scanf( %d , &n);     int a[n], b[n];     long int s = 0;     for (int i = 0; i < n; i++) scanf( %d%d , &a[i], &b[i]);     for (int i = 1; i < n; i++) {       if (b[i] >= b[i - 1]) b[i] = b[i - 1];       s += (a[i] * b[i]);     }     printf( %ld n , s + (a[0] * b[0]));     return 0;   }   