#include <iostream>
using namespace std;

int main() {
    int n, ans = 0;
    auto mod = [](long long x){return x % 1000000007;};
    cin >> n;
    for (int i = 0; i < n; i++) {
        long long c, d;
        cin >> c >> d;
        c = mod((c+1)/2);
        d = mod(d);
        ans = mod(ans + c * d);
    }
    cout << ans << endl;
    return 0;
}