#include<iostream>
using namespace std;

int main(){
	int x1,y1,x2,y2;
	cin >> x1 >> y1 >> x2 >> y2;

	int result = max(x1,y1);
	if(x1 == 0){
		result += (x2 == 0 && y2 < y1);
	}else if(y1 == 0){
		result += (y2 == 0 && x2 < x1);
	}else if(x1 == y1){
		result += (x2 == y2 && x2 < x1);
	}

	cout << result << endl;
}