using System;
using System.IO;
using System.Linq;
using System.Collections.Generic;
using System.Text;

public class Program
{

    public void Proc()
    {
        int keta = int.Parse(Reader.ReadLine());
        long max = Convert.ToInt64("1".PadRight(keta, '0'), 2);
        long hp = long.Parse(Reader.ReadLine());
        long kougeki = long.Parse(Reader.ReadLine());
        long kaihuku = long.Parse(Reader.ReadLine());

        long ans = hp / kougeki;
        if(hp%kougeki!=0) {
            ans++;
        }
        long ans2 = (max - hp) / kaihuku;
        if((max-hp)%kaihuku!=0) {
            ans2++;
        }
        ans = Math.Min(ans, ans2);
        Console.WriteLine(ans);
    }



    public class Reader
    {
        private static StringReader sr;
        public static bool IsDebug = false;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (sr == null)
                {
                    sr = new StringReader(InputText.Trim());
                }
                return sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
        private static string InputText = @"





26
16777221
20
20




";
    }

    public static void Main(string[] args)
    {
#if DEBUG
        Reader.IsDebug = true;
#endif
        Program prg = new Program();
        prg.Proc();
    }
}