#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int x, y, a, b;
    cin >> x >> y >> a >> b;
    int ans = max(abs(x), abs(y));

    if(abs(x) == abs(y) && abs(a) == abs(b) && abs(a) < abs(x)){
        x = x / abs(x);
        y = y / abs(y);
        a = a / abs(a);
        b = b / abs(b);
        if(x == a && y == b)ans++;
    }
    
    cout << ans << endl;
}