import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		long []C = new long[N];
		long []D = new long[N];
		for(int i = 0; i < N; i++) {
			C[i] = scan.nextLong();
			D[i] = scan.nextLong();
		}
		scan.close();
		long sum = 0;
		for(int i = 0; i < N; i++) {
			long k;
			if(C[i] % 2 == 0) {
				k =  C[i] / 2;
			}else {
				k = C[i] / 2 + 1;
			}
			sum += k * D[i];
		}
		long ans = sum % (1000000007);
		System.out.println(ans);
	}
}