include <bits/stdc++.h>

using namespace std;

int main () {

int a, b, c, d, f, g, sum;
cin >> a >> b >> c >> d;
f = a - c;
if (f < 0)
	f = -f;
else
	f = f;
g = b - d;
if (g < 0)
	g = -g;
else
	g = g;
sum = f + g;
cout << sum;
return 0;

}