import java.util.Scanner;

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