#include "bits/stdc++.h"
using namespace std;

typedef long long ll;
ll x, y;


int main() {
	cin >> x >> y;
	int x2,y2;
	cin >> x2 >> y2;

	if (x == y && x2 == y2 && x<x2) {
		cout << x+1 << endl;
	}
	else {
		cout << max(abs(x), abs(y)) << endl;
	}
}