#include <bits/stdc++.h>
using namespace std;

unsigned long long mod = 1000000007;


int main(){
	int N;
	cin >> N;
	unsigned long long ans = 0;
	for(int i = 0 ; i < N ; i++){
		unsigned long long C,D;
		cin >> C >> D;
		long long B = (C+1)/2;
		ans += B % mod * D % mod;
		ans %= mod;
	}
	cout << ans << endl;
}