#include <iostream>
using namespace std;
const long long MOD = 1000000007;
int main(){
	int N;
	cin >> N;
	int ans = 0;
	for (int i = 0; i < N; i++){
		long long C, D;
		cin >> C >> D;
		C = (C + 1) / 2;
		ans += (C % MOD) * (D % MOD) % MOD;
		ans %= MOD;
	}
	cout << ans << endl;
}