Untitled

#include<stdio.h>
#include<stdlib.h>

int main(){
	int a, b, c, d, e, f, g, h;
	scanf("%d %d %d %d %d %d %d %d", &a, &b, &c, &d, &e, &f, &g, &h);
	int w=c-a, x=d-b, y=g-a, z=h-b;
	int ans=w*z-x*y;
	if(ans <0) printf("%d", -ans);
	else printf("%d", ans);
	return 0;
}