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

int main() {
	int x, y, x2, y2;
	cin >> x >> y >> x2 >> y2;
	int ans = -1;
	if (abs(x2) < abs(x) && abs(y2) < abs(y)) {
		if (x == 0 && x2 == 0) {
			ans = abs(y) + 1;
		}
		else if (y == 0 && y2 == 0) {
			ans = abs(x) + 1;
		}
		if (abs(x) == abs(y) && abs(x2) == abs(y2) && x / abs(x) == x2 / abs(x2) && y / abs(y) == y2 / abs(y2)) {
			ans = abs(x) + 1;
		}
	}
	if(ans==-1) {
		ans = max(abs(x), abs(y));
	}
	cout << ans << endl;
	return 0;
}