defmodule Main do
  def main do
    k = IO.gets("") |> String.trim |> String.to_integer
    [a, b] =
      IO.read(:line)
      |> String.trim
      |> String.split(" ")
    a = String.to_integer(a)
    b = String.to_integer(b)
    mx = b / k * k
    if a <= mx do 
    IO.puts("OK") 
    else 
    IO.puts("NG") 
    end
  end
end
    
