include

include

using namespace std; int main(void){

//freopen("1126.in","r",stdin);
//freopen("1126.out","w",stdout);
int x1,y1,x2,y2,xc,yc;
scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
xc=x1-x2;
if(xc>=0){
	xc=xc;
}else{
	xc=xc*-1;
}
yc=y1-y2;
if(yc>=0){
	yc=yc;
}else{
	yc=yc*-1;
}
printf("%d",xc+yc);
return 0;

}