#include <bits/stdc++.h>
using namespace std;
int main() {
	long long x1, y1, x2, y2;
	cin >> x1 >> y1 >> x2 >> y2;
	long long a = abs(x1 - x2);
	long long b = abs(y1 - y2);
	if (a % 2 != b % 2) {
		cout << -1;
		return 0;
	}else {
		if (a > b) swap(a, b);
		if (a == 1) {
			if (x1 < x2 && y1 > y2 || x1 > x2 && y1 < y2) {
				cout << b + 2;
				return 0;
			}else {
				cout << b;
				return 0;
			}
		}
		if (a % 2 == 0) {
			cout << b + a;
		}else {
			cout << b + a - 1;
		}
	}
	return 0;
}