#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)

int main()
{
	int x, y; cin >> x >> y;
	int x2, y2; cin >> x2 >> y2;
	
	int ans = max(x, y);
	if (x == y && x2 == y2)
	{
		if (min(x, 0) < x2 && x2 < max(x, 0)) ans++;
	}
	cout << ans << endl;
}