#include "bits/stdc++.h"

using namespace std;

signed main() {

	int px, py, qx, qy;
	cin >> px >> py >> qx >> qy;
	int sec = (abs(px - qx) + abs(qx - qy)) / 2;
	if ((abs(px - qx) + abs(qx - qy)) % 2 != 0) {
		sec++;
	}
	cout << sec << endl;

}