#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>
#include<cmath>
using namespace std;
int n,m,x,y;
int main()
{
cin>>n>>m>>x>>y;
if(n>m) swap(n,m);
if(x>y) swap(x,y);
cout<<min(m-n,abs(n - x)+abs(y -m))<<endl;
}