import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        int[] arr = new int[n];
        for (int i = 0; i < n - 1; i++) {
            arr[i] = Integer.parseInt(br.readLine());
        }
        int num = 0;
        long total = 0;
        for (int i = 0; i < n - 1; i++) {
            String[] line = br.readLine().split(" ", 2);
            int b = Integer.parseInt(line[0]);
            int c = Integer.parseInt(line[1]);
            num += c - b;
            total += num * arr[i];
        }
        System.out.println(total);
    }
}