import java.util.Scanner;

public class Main{
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
    
		//键入数值
		long x1=sc.nextLong();
		long y1=sc.nextLong();
		long x2=sc.nextLong();
		long y2=sc.nextLong();
		long x3=sc.nextLong();
		long y3=sc.nextLong();
		long x4=sc.nextLong();
		long y4=sc.nextLong();
		//计算两矩阵面积之和
		long s=(x2-x1)*(y2-y1)+(x4-x3)*(y4-y3);
		//计算重叠面积
		//画图找规律
		long a=Math.max(0, Math.min(x2, x4)-Math.max(x1, x3));
		long b=Math.max(0, Math.min(y2, y4)-Math.max(y1, y3));
		//输出结果
		System.out.print(s-a*b);
	}
}