#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<vector>
#include<map>
#include<queue>
#include<string>
#include<sstream>
#include<cmath>
#include<numeric>
using namespace std;

int main(){

  int n;
  cin >> n;

  long long int cnt = 0;
  long long int c, d;
  for(int i=0; i<n; i++){
    cin >> c >> d;
    if( c%2 == 0 ) cnt += d*( c/2 );
    else cnt += d*( c/2 + 1 );
  }
  cnt %= 1000000007;
  cout << cnt << endl;


  return 0;
}