N, M = gets.split.map(&:to_i)
X, Y = gets.split.map(&:to_i)
x, y = [X, Y].map {|a|
  b = (a - 1) % (2 * M)
  if b < M
    b
  else
    2 * M - (b + 1)
  end
}
ans = if x == y
        "YES"
      else
        "NO"
      end
puts ans