#include <iostream>
#include <cstdlib>
#include <algorithm>

using namespace std;

int sign(int x) {
	return (0 < x) - (x < 0);
}

int main() {
	int x, y, x2, y2;
	cin >> x >> y >> x2 >> y2;
	int result = min(abs(x), abs(y)) + abs(x - y);
	if (x == y && x2 == y2 
		&& abs(x2) < abs(x) 
		&& sign(x) == sign(x2) && sign(y) == sign(y2)) {
		++result;
	}
	cout << result << endl;
	return 0;
}