#include <iostream>
#include<cstdlib>
#include<algorithm>
using namespace std;

int main()
{
	int x, y, x2, y2; cin >> x >> y >> x2 >> y2;
	bool flag = true;
	if (x > 0)if (x2 < 0)flag = false;
	else if (x < 0)if (x2>0)flag = false;
	if (y>0)if (y2 < 0)flag = false;
	else if (y < 0) if (y2>0)flag = false;
	
	cout << max(abs(x),abs(y)) + (abs(x)>abs(x2)&&abs(x2)==abs(y2)&&abs(x)==abs(y)&&flag)<< endl;

	return 0;
}