#include <stdio.h>

int abs(int n){
	if(n<0){
		return -1*n;
	}
	return n;
}

int getSymbol(int n){
	if(n<0){
		return -1;
	}else if(n>0){
		return 1;
	}else{
		return 0;
	}
}

int main(void){
	int ex, ey;
	int tx, ty;
	int dis;
	
	
	scanf("%d %d", &tx, &ty);
	scanf("%d %d", &ex, &ey);
	
	if(abs(tx) > abs(ty)){
		dis = abs(tx);
	}else{
		dis = abs(ty);
	}
	
	if(ex == ey && tx == ty && getSymbol(ex) == getSymbol(tx) && getSymbol(ey) == getSymbol(ty)){
		if(abs(tx) > abs(ex)){
			dis += 1;
		}
	}
	
	printf("%d\n", dis);
	
	return 0;
}