#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 = 0;
	if (x == 0) {
		if (x2 == 0) {
			if (y>0&&y2>0&&y<y2||y<0&&y2<0&&y>y2) {
				ans = abs(y);
			}
			else {
				ans = abs(y) + 1;
			}
		}
		else {
			ans = abs(y);
		}
	}else if (y == 0) {
		if (y2 == 0) {
			if (x>0 && x2>0 && x<x2 || x<0 && x2<0 && x>x2) {
				ans = abs(x);
			}
			else {
				ans = abs(x) + 1;
			}
		}
		else {
			ans = abs(x);
		}
	}
	else if (x == y && x2 == y2) {
		if (x > 0 && x2 > 0 && x < x2 || x < 0 && x2<0 && x>x2) {
			ans = abs(x);
		}
		else {
			ans = abs(x) + 1;
		}
	}
	else if (x == -y && x2 == -y2) {
		if (x > 0 && x2 > 0) {
			if (x < x2) {
				ans = abs(x);
			}
			else {
				ans = abs(x) + 1;
			}

		}
		else if (x < 0 && x2 < 0) {
			if (x > x2) {
				ans = abs(x);
			}
			else {
				ans = abs(x) + 1;
			}
		}
		else {
			ans = abs(x);
		}
	}
	else {
		ans = max(abs(x), abs(y));
	}
	cout << ans << endl;

	return 0;
}