#include <bits/stdc++.h>
using namespace std;

int main() {
    int sx, sy, tx, ty;
    cin >> sx >> sy >> tx >> ty;

    auto dist = [](int x1, int y1, int x2, int y2) {
        return max(abs(x1 - x2), abs(y1 - y2));
    };

    int ans = dist(0, 0, sx, sy);
    if (sx == sy && tx == ty && sx > tx)
        ans++;
    cout << ans << endl;
}