#include <iostream>
#include <cmath>
using namespace std;

int main(){
  ios::sync_with_stdio(false);
  double n, c, d, total=0;

  cin >> n;
  for(int i=0; i<n; ++i){
    cin >> c >> d;
    c=ceil(c/2);
    total+=c*d;
  }
  total=fmod(total, pow(10, 9)+7);
  cout << total << "\n";

  return 0;
}