{-# LANGUAGE PartialTypeSignatures #-}
module Main (main) where

import qualified Data.ByteString.Char8 as C8
import Data.Bool
import qualified Data.Char as C
import qualified Data.List as L

main :: IO ()
main = do
  [k] <- readInts
  readInts >>= output . solve k

solve :: Int -> [Int] -> _
solve k [a,b]
  | k == 1 = True
  | otherwise = (b-a `div` k) >= 1

output :: _ -> IO ()
output = putStrLn . bool "NG" "OK"

-- utils
readInts :: IO [Int]
readInts = L.unfoldr (C8.readInt . C8.dropWhile C.isSpace) <$> C8.getLine