#include<iostream>
#include<vector>

int main() 
{
	int desk_num;

	std::cin >> desk_num;
	std::vector<long long> chest(desk_num);

	long long students = 0;
	for (int i = 0; i < desk_num; i++)
	{
		long long chest_num, desk_num;
		std::cin >> chest_num >> desk_num;
		students += ((chest_num + 1) / 2) * desk_num;
	}

	std::cout << students % 1000000007 << std::endl;

	return 0;
}