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

int main()
{
	int N;
	cin >> N;
	vector<long long> C( N );
	vector<long long> D( N );
	for( int i = 0; i < N; i++ ) {
		cin >> C[i] >> D[i];
	}

	const long long m = 1000000000 + 7;
	long long ans = 0;
	for( int i = 0; i < N; i++ ) {
		long long c = C[i] / 2;
		if( C[i] % 2 ) c++;
		c %= m;
		D[i] %= m;
		ans += c * D[i] % m;
		ans %= m;
	}

	cout << ans << endl;
}