#include <iostream>
using namespace std;

int main() {
int x, y, xx, yy; cin >> x >> y >> xx >> yy;
cout << max(x, y) + (abs(x) == abs(y) && abs(xx) == abs(yy) && x * xx >= 0 && y * yy >= 0 && !(x == 0 && y == 0) && xx < x);
return 0;
}