#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <functional>
#include <set>
#include <sstream>
#include <map>
#include <queue>
#include <stack>

using namespace std;


int main()
{
		
	long long x,y,x2,y2;
	cin>>x>>y>>x2>>y2;
	
	long long res=max(abs(x),abs(y));
	int way1,way2;
	
	if(x>=0 && y>=0) way1=0;
	if(x<=0 && y>=0) way1=1;	
	if(x<=0 && y<=0) way1=2;
	if(x>=0 && y<=0) way1=3;	

	if(x2>=0 && y2>=0) way2=0;
	if(x2<=0 && y2>=0) way2=1;	
	if(x2<=0 && y2<=0) way2=2;
	if(x2>=0 && y2<=0) way2=3;	
	
	if(x==y && x2==y2 && max(abs(x),abs(y))>max(abs(x2),abs(y2)) && way1==way2) res++;

	cout<<res<<endl;
	

	return 0;
}