#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <cstring>

typedef long long ll;
using namespace std;

#define mod 1000000007
#define INF 1000000000 //(int)1e9
#define LLINF 2000000000000000000 //(ll)2e18
#define PI  3.1415926536

#define SIZE 100000

int gcd(int a,int b){
    if(a==0)
        return b;
    return gcd(b%a,a);
}

int sign(int x){
    return (x>0)-(x<0);
}

int main(){
    int x,y,x2,y2;
    int a,b,ans;
    
    cin >> x >> y >> x2 >> y2;
    
    ans = max(abs(x),abs(y));
    
    if(x==y && x2==y2 && x2<x){
        ans+=1;
    }
    
    cout << ans << endl;
    
    
    return 0;
}