import java.util.Scanner;

public class Main {
	public static void main(String[] a) {
		Scanner s = new Scanner(System.in);
		long N=s.nextInt(),i=0,z=0;
		while(i++<N){
			long c=s.nextLong(), d=s.nextLong()%1000000007;
			c=(c/2+c%2)%1000000007;
			z=(z+c*d)%1000000007;
		}
		System.out.println(z);
	}
}