#include <iostream>

using namespace std;

int main() {
	int n, m, x, y, px, py;
	cin >> n >> m >> x >> y;
	if (m > n) {
		n = m + n;
		m = n - m;
		n = n - m;
	}
	px = m - x;
	py = n - y;
	if (x < y && x < px && x < py) {
		cout << x;
	}
	else if (y < x && y < px && y < py) {
		cout << y;
	}
	else if (px < x && px < y && px < py) {
		cout << px;
	}
	else {
		cout << py;
	}
	return 0;
}