#include <bits/stdc++.h>
using namespace std;

int main() {
  int N, M = 1e9+7;
  cin >> N;
  long long ans = 0, c, d;
  for (int i = 0; i < N && cin >> c >> d; i++) (ans += d * ((c + 1) / 2)) % M;
  cout << ans << "\n";
}