include<stdio.h>

int main(){

int x1,y1,x2,y2,xc,yc; scanf("%d%d%d%d",&x1,&y1,&x2,&y2); xc=x1-x2;
if(xc>=0){

}else{
	xc=xc*-1;
	} yc=y1-y2;
	if(yc>=0){
		yc=yc;
	}else{
		yc=yc*-1;
	}
printf("%d",xc+yc);
return 0; 

}