main = do
  li <- getLine
  let k = read li
  li <- getLine
  let [a,b] = map read $ words li
  let ans = compute k a b
  putStrLn $ if ans then "OK" else "NG"

compute :: Int -> Int -> Int -> Bool
compute k a b = a1 <= b
  where
    a1 = (a + k - 1) `div` k * k
