#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
typedef long long ll;

int main() {
	ll x1, y1, x2, y2;
	cin >> x1 >> y1 >> x2 >> y2;
	ll ans = max(x1, y1);
	if(abs(x1) == abs(y1) && abs(x1) > abs(x2) && x1*y2 - x2*y1 == 0) {
		ans++;
	}
	cout << ans << endl;
}