#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 ansx=abs(x-x1),ansy=abs(y-y1),ans=ansx+abs(ansx-ansy);
	if(ansx==ansy)ans++;
	printf("%d\n",ans);  
	return 0;
}