#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <vector>
#include <queue>
#include <string>
#include <functional>
#include <iostream>


using namespace std;
 
//namaega184 
 
int main(){
	
	int x,y,x1,y1;scanf("%d%d%d%d",&x,&y,&x1,&y1);
	int ans=max(x,y);if(abs(x)==abs(y)&&!(x>0^x1>0)&&!(y>0^y1>0)&&abs(x)>abs(x1)&&abs(y)>abs(y1)&&abs(x1)==abs(y1))ans++;
	printf("%d\n",ans);  
	return 0; 
}