#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int main() {
    llong x, y, x2, y2;
    cin >> x >> y >> x2 >> y2;

    if(x == y && x2 == y2 && x*x2 >= 0 && abs(x) > abs(x2)) {
        cout << x+1 << "\n";
    } else {
        cout << max(abs(x), abs(y)) << "\n";
    }
}