#include <iostream>
using namespace std;

int main()
{
	int n;
	unsigned long long int c, d, an = 0;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> c >> d;
		if (c % 2 == 0)
		{
			an += ((c / 2) * d) % 1000000007;
		}
		else
		{
			an += ((c / 2 + 1) * d) % 1000000007;
		}
	}
	cout << an << endl;
}