#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int main() {
    // Input
    int N;
    cin >> N;
    vector<long long> C(N), D(N);
    rep(i, N) cin >> C[i] >> D[i];

    // Calculation
    long long ans = 0;
    const long long MOD = 1'000'000'007;
    rep(i, N) {
        int able = (C[i] + 1) / 2;
        ans = (ans + (able % MOD) * (D[i] % MOD) % MOD) % MOD;
    }

    // Output
    cout << ans << endl;
}