#include<bits/stdc++.h>
using namespace std;
#define inf INT_MAX
#define INF LLONG_MAX
#define ll long long
#define ull unsigned long long
#define M (int)(1e9+7)
#define P pair<int,int>
#define PLL pair<ll,ll>
#define FOR(i,m,n) for(int i=(int)m;i<(int)n;i++)
#define RFOR(i,m,n) for(int i=(int)m;i>=(int)n;i--)
#define rep(i,n) FOR(i,0,n)
#define rrep(i,n) RFOR(i,n,0)
#define all(a) a.begin(),a.end()
#define IN(a,n) rep(i,n){ cin>>a[i]; }
const int vx[4] = {0,1,0,-1};
const int vy[4] = {1,0,-1,0};
#define PI 3.14159265
#define F first
#define S second
#define PB push_back
#define EB emplace_back
#define int ll
#define vi vector<int>



signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int x,y,x2,y2;
  cin>>x>>y>>x2>>y2;

  if(abs(x)==abs(y)&&abs(x2)==abs(y2)&&x*x2>0&&y*y2>0&&x*(x2-x)<0){
    cout<<abs(x)+1<<endl;
  }else{
    cout<<max(abs(x),abs(y))<<endl;
  }

}