using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		
		if(A[1]==B[1]){
			if(Math.Abs(B[0])>Math.Abs(A[0])){
				Console.WriteLine(Math.Abs(A[0]));
			}else{
				Console.WriteLine(Math.Abs(A[0]));
			}
			return;
		}
		if(A[0]==B[0]){
			if(Math.Abs(B[1])>Math.Abs(A[1])){
				Console.WriteLine(Math.Abs(A[1]));
			}else{
				Console.WriteLine(Math.Abs(A[1]));
			}
			return;
		}
		if(A[0]==A[1]&&B[0]==B[1]){
			if(Math.Abs(B[1])>Math.Abs(A[1])){
				Console.WriteLine(Math.Abs(A[1]));
			}else if(A[0]*B[0]<0){
				Console.WriteLine(Math.Abs(A[1]));
			}else{
				Console.WriteLine(Math.Abs(A[1])+2);
			}
			return;
		}
		if(A[0]==-A[1]&&B[0]==-B[1]){
			if(Math.Abs(B[1])>Math.Abs(A[1])){
				Console.WriteLine(Math.Abs(A[1]));
			}else if(A[0]*B[0]<0){
				Console.WriteLine(Math.Abs(A[1]));
			}else{
				Console.WriteLine(Math.Abs(A[1])+2);
			}
			return;
		}
		
		
		
		if(A[0]<0)A[0]*=-1;
		if(A[1]<0)A[1]*=-1;
		Console.WriteLine(A.Max());
		return;
		
	}
	long[] A,B;
	public Sol(){
		A=rla();B=rla();
	}




	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
}