#include <cmath>
#include <iostream>
using namespace std;

int main() {
	int N;
	cin >> N;
	long long ans = 0;
	for (int i = 0; i < N; i++) {
		long long C, D;
		cin >> C >> D;
		ans += (((long long)ceil(C / 2.0) % 1000000007LL) * (D % 1000000007LL)) % 1000000007LL;
		ans %= 1000000007LL;
	}
	cout << dec << ans << endl;
	return 0;
}