import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	long[] prices = new long[n - 1];
    	for (int i = 0; i < n - 1; i++) {
    	    prices[i] = sc.nextInt();
    	}
    	long total = 0;
    	int current = 0;
    	for (int i = 0; i < n - 1; i++) {
    	    current -= sc.nextInt() - sc.nextInt();
    	    total += current * prices[i];
    	}
    	System.out.println(total);
    }
}