#include <bits/stdc++.h>
using namespace std;
class Solver {
  public:
    bool solve() {
        int x, y; cin >> x >> y;
        int xe, ye; cin >> xe >> ye;
        int ans = max(abs(x), abs(y));

        if(abs(x) == abs(y) and abs(xe) == abs(ye)) {
            if(x * xe >= 0 and y * ye >= 0) {
                if(abs(x) > abs(xe)) ans += 1;
            }
        }
        
        cout << ans << endl;
        return 0;
    }
};

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    Solver s;
    s.solve();
    return 0;
}