#include <bits/stdc++.h> 

using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;

int main() {
    ll ans = 0;
    int N;
    cin >> N;
    for (int i = 0; i < N; i++) {
        ll Ci, Di; cin >> Ci >> Di;
        ll num = Ci / 2 + Ci % 2;
        ll CiDi = (num * Di) % MOD;
        ans = (ans + CiDi) % MOD;
    }
    cout << ans << endl;
}