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

namespace yuki0715_C
{
    class Program
    {
        static void Main(string[] args)
        {
            var l1 = getsplit();
            var l2 = getsplit();
            int n = int.Parse(l1[0]);
            int m = int.Parse(l1[1]);
            int x = int.Parse(l2[0]);
            int y = int.Parse(l2[1]);
            int tc = 0;
            int hc = 0;
            string muki = "nobori";


            while (tc==0)
            {
                
                if (muki=="nobori")
                {
                    if (x-m<=0)
                    {
                        tc = x;
                    }
                    else
                    {
                        x -= m;
                    }
                   
                    muki = "kudari";
                }
                else 
                {
                    if (x - m <= 0)
                    {
                        tc = m-x+1;
                    }
                    else
                    {
                        x -= m;
                    }
                   
                    muki = "nobori";
                }
            }

            muki = "nobori";
            while (hc == 0)
            {
              
                if (muki == "nobori")
                {
                   
                    if (y - m <= 0)
                    {
                        hc = y;
                    }
                    else
                    {
                        y -= m;
                    }
                    muki = "kudari";
                }
                else 
                {
                   
                    if (y - m <= 0)
                    {
                        hc = m - y + 1;
                    }
                    else
                    {
                        y -= m;
                    }
                    muki = "nobori";
                }
            }
            
            if (tc == hc)
            {
                Console.WriteLine("YES");
            }
            else
            {
                Console.WriteLine("NO");
            }
        }
        public static string[] getsplit()
        {
            string[] x = Console.ReadLine().Split(' ');
            return x;
        }
        public static int getint()
        {
            int x = int.Parse(Console.ReadLine());
            return x;
        }
    }
}