#!/usr/bin/env perl

use strict;
use warnings;

my ($n, $m) = split/ /, <>; chomp $m;
my ($x, $y) = split/ /, <>; chomp $y;
$x--; $y--;
my $pat1 = int($x / $m);
my $pat2 = int($y / $m);

sub check {
  if ($pat1 % 2 == $pat2 % 2) {
    $x % $m == $y % $m;
  } else {
    $x % $m == $m - ($y % $m) - 1;
  }
}

print check ? "YES\n" : "NO\n";