import java.util.*;

public class Main{
    static long x1,y1,x2,y2,x3,y3,x4,y4;

    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        x1 = sc.nextLong();
        y1 = sc.nextLong();
        x2 = sc.nextLong();
        y2 = sc.nextLong();
        x3 = sc.nextLong();
        y3 = sc.nextLong();
        x4 = sc.nextLong();
        y4 = sc.nextLong();

        long sum = (x2 - x1) * (y2 - y1) + (x4 -x3) * (y4 - y3);
        long sum2 = 0;

        if(x3 < x2 && y3 < y2 && x1 < x4 && y1 < y4){
            long x11 = Math.max(x1, x3);
            long y11 = Math.max(y1, y3);
            long x22 = Math.min(x2, x4);
            long y22 = Math.min(y2, y4);
            sum2 = (x22 - x11) * (y22  - y11);
        }


        System.out.println(sum - sum2);
    }
}