import java.util.Scanner;
public class Test{
	public static void main(String[] arg){
		Scanner sc = new Scanner(System.in);
		int n;
		n = sc.nextInt();
		Long res = (long)0;
		Long[] c = new Long[n];
		Long[] d = new Long[n];
		for(int i = 0;i<n;i++){
			c[i] = sc.nextLong();
			if(c[i] % 2 == 0){
				c[i] = (c[i] / 2) % 1000000007;
			}else{
				c[i] = (c[i] / 2 +1) % 1000000007;
			}
			d[i] = sc.nextLong() % 1000000007;
			res = (res + c[i] * d[i] )% 1000000007;
		}
		System.out.println(res);
	}
}