let golf k a b =
  let a_mod_k = a mod k in
  if a_mod_k = 0 then "OK"
                 else if b - (a - a_mod_k + k) > 0 then "OK" else "NG"

let k = read_int ()
let a, b = Scanf.sscanf (read_line()) "%d %d" (fun a b -> (a, b))
let () = Printf.printf "%s\n" (golf k a b)
