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

#define ABS(x) ((x)>0?(x):-(x))
#define MAX(a,b) ((a)>(b)?(a):(b))

typedef long long int ln;

int main(void){

	int x,y;
	int x2,y2;
	scanf("%d%d%d%d",&x,&y,&x2,&y2);

	if(ABS(x)==ABS(y) && ABS(x2)==ABS(y2) && ABS(x)>ABS(x2) && x/ABS(x)==x2/ABS(x2) && y/ABS(y)==y2/ABS(y2)){
		printf("%d\n",ABS(x)+1);
	} else {
		printf("%d\n",MAX(ABS(x),ABS(y)));
	}
	return 0;
}