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;
            


            while (true)
            {
                if (x - m <= 0)
                {
                    tc = x;
                    break;
                }
                x -= m;
                
                if (x - m <= 0)
                {
                    tc = m - x + 1;
                    break;
                }
                x -= m;
            }

        
            while (true)
            {
                if (y - m <= 0)
                {
                    hc = y;
                    break;
                }
                y -= m;
                if (y - m <= 0)
                {
                    hc = m - y + 1;
                    break;
                }
                y -= m;                 
            }
            
            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;
        }
    }
}