#include<stdio.h>

int max(int a,int b){
	if(a>b){return a;}else{return b;}
}

int main(void){
	int x,y,x2,y2,p;
	scanf("%d %d %d %d",&x,&y,&x2,&y2);

	p=0;

	if(x==y && x2==y2 && x>0 && x2>0 && x2<x){p=1;}
	if(x==y && x2==y2 && x<0 && x2<0 && x2>x){p=1;}
	if(x==-y && x2==-y2 && x>0 && x2>0 && x2<x){p=1;}
	if(x==-y && x2==-y2 && x<0 && x2<0 && x2>x){p=1;}

	printf("%d\n",max(max(x,-x),max(y,-y))+p);
}