#include <algorithm>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <sstream>
#include <functional>
#include <map>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <list>
#include <numeric>
using namespace std;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const int INF = 1<<25;
typedef pair<int,int> P;
typedef long long ll;
typedef unsigned long long ull;
ll a, b, c, d, a2, b2, c2, d2;

bool block(){
	if(a==0){
		if(c!=0) return false;
		return b*d>0;
	}
	if(c2!=d2) return false;
	return a*c>0 && b*d>0;
}

int main(){
	a, b, c, d;
	cin>>a>>b>>c>>d;
	if(abs(a)>abs(b)){
		swap(a, b);
		swap(c, d);
	}
	a2 = abs(a), b2 = abs(b), c2 = abs(c), d2 = abs(d);
	ll res = max(a2, b2);
	if(a2!=b2 && min(a2, b2)>0) cout<<res<<endl;
	else if(block()) cout<<res+1<<endl;
	else cout<<res<<endl;
	return 0;
}