#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

const ll mod = 1e9 + 7;

int main(void) {
  int n;
  cin >> n;

  ll ans = 0;
  for (int i = 0; i < n; i++) {
    ll c, d;
    cin >> c >> d;
    ans += (c + 2 - 1) / 2 * d;
    ans %= mod;
  }

  cout << ans << endl;

  return 0;
}