#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

ll N, C, D, ans;
ll mod = 1000000007;

int main() {
  cin >> N;
  for (int i = 0; i < N; i++) {
    cin >> C >> D;
    if (C % 2 == 1) ans = (ans + (((C + 1) / 2) % mod * D % mod) % mod) % mod;
    else ans = (ans + ((C / 2) % mod * D % mod) % mod) % mod;
  }
  cout << ans << endl;
  return 0;
}