#include <bits/stdc++.h>
using namespace std;
template <class A, class B>
ostream& operator<<(ostream& o, const pair<A, B>& p) {
  return o << "(" << p.first << ", " << p.second << ")";
}
template <class T>
ostream& operator<<(ostream& o, const vector<T>& v) {
  o << "[";
  for (__typeof((v).end()) it = (v).begin(); it != (v).end(); ++it)
    o << *it << ", ";
  return o << "]";
}
template <class T>
ostream& operator<<(ostream& o, const set<T>& v) {
  o << "[";
  for (__typeof((v).end()) it = (v).begin(); it != (v).end(); ++it)
    o << *it << ", ";
  return o << "]";
}
template <class T>
inline void MAX(T& a, T b) {
  if (a < b) a = b;
}
template <class T>
inline void MIN(T& a, T b) {
  if (a > b) a = b;
}
template <class T>
inline bool read(T& x) {
  int c = getchar();
  int sgn = 1;
  while (~c && c < '0' || c > '9') {
    if (c == '-') sgn = -1;
    c = getchar();
  }
  for (x = 0; ~c && '0' <= c && c <= '9'; c = getchar()) x = x * 10 + c - '0';
  x *= sgn;
  return ~c;
}
int main() {
  int n;
  cin >> n;
  int total = 0;
  int min_cost;
  for (int i = 1; i <= n; i++) {
    int a, b;
    cin >> a >> b;
    if (i == 1) {
      if (a > 0) {
        total += (b * a);
      }
      min_cost = b;
    } else if (b > min_cost) {
      total += (min_cost * a);
    } else {
      min_cost = b;
      total += (min_cost * a);
    }
  }
  cout << total;
}
