1234567891011#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
int main(){
	int a,b,x,y; cin >> a >> b >> x >> y;
	if(x > y) swap(x,y);
    if(a > b) swap(a,b);
	cout << min(b - a,abs(x - a) + abs(y - b));//取用传送门和不用传送门的最短距离 
	return 0;
}