import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[]a = new int[n];
		int[]b = new int[n];
		int[]c = new int[n];
		for(int i = 0; i < n - 1; i++) {
			a[i] = scan.nextInt();
		}
		for(int i = 0; i < n; i++) {
			b[i] = scan.nextInt();
			c[i] = scan.nextInt();
		}
		scan.close();
		int sum = 0;
		int B = 0;
		int C = 0;
		for(int i = 0; i < n; i++) {
			B += b[i];
			C += c[i];
			sum += a[i] * (C - B);
		}
		System.out.println(sum);
	}
}