using System;
using System.Linq;

public class Program
{
	public static void Main()
	{
		int[] NM = Console.ReadLine().Split().Select(i => int.Parse(i))
			.ToArray();
		int N = NM[0];
		int M = NM[1];
		int[] XY = Console.ReadLine().Split()
			.Select(i => int.Parse(i) % (2 * M)).OrderBy(i => i).ToArray();
		if (XY[0] == XY[1] || XY[0] == 2 * M - XY[1] + 1)
		{
			Console.WriteLine("YES");
		}
		else
		{
			Console.WriteLine("NO");
		}
	}
}