using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Oushou_CS
{
    class Program
    {
        static void Main(string[] args)
        {
            Sol mysol = new Sol();
            mysol.Solve();
#if DEBUG
            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
#endif
        }
    }

    class Sol
    {
        public void Solve()
        {
            int ans = ChebyshevDistance(0, 0, x, y);
            if(isObstacle(x,y,x2, y2))
            {
                ans++;
            }
            Console.WriteLine(ans.ToString());
        }

        int x, y, x2, y2;

        public Sol()
        {
            int[] xy = ria();
            x = xy[0];
            y = xy[1];
            int[] xy2 = ria();
            x2 = xy2[0];
            y2 = xy2[1];
        }

        static int ChebyshevDistance(int x1, int y1, int x2, int y2)
        {
            return Math.Max(Math.Abs(x1 - x2), Math.Abs(y1 - y2));
        }

        // 象限を返す（0があるときも返す）
        static int Quadrant(int x, int y)
        {
            if (x > 0)
            {
                if (y > 0)
                {
                    return 1;
                }
                else
                {
                    return 4;
                }
            }
            else
            {
                if (y > 0)
                {
                    return 2;
                }
                else
                {
                    return 3;
                }
            }
        }

        static bool isObstacle(int x, int y, int x2, int y2)
        {
            int q1 = Quadrant(x, y);
            if ((Math.Abs(x) == Math.Abs(y)) && (Math.Abs(x2) == Math.Abs(y2)) && (q1 == Quadrant(x2, y2)))
            {
                int t = x - x2;
                if (((q1 == 1 || q1 == 4) && t>0) || ((q1 == 2 || q1 == 3) && t<0))
                {
                    return true;
                }
            }
            return false;
        }

        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 Console.ReadLine().Split(' ').Select(e => int.Parse(e)).ToArray(); }
        static long[] rla() { return Console.ReadLine().Split(' ').Select(e => long.Parse(e)).ToArray(); }
        static double[] rda() { return Console.ReadLine().Split(' ').Select(e => double.Parse(e)).ToArray(); }
    }
}