module FMath = struct
  let is_prime n =
    if n < 2 then false
    else if n = 2 then true
    else if ((n mod 2) = 0) then false
    else
      let sqrt_n = (int_of_float (sqrt (float_of_int n)) + 1) in
      let rec rec_is_prime p =
        let p2_1 = (p * 2) + 1 in
        if (p2_1 > sqrt_n) then true
        else if ((n mod p2_1) = 0) then false
        else rec_is_prime (p + 1) in
      rec_is_prime 1;;

  let primes limit =
    let rec acc n result =
      if (n = limit) then result
      else if (is_prime n) then acc (n + 1) (n :: result)
      else acc (n + 1) result in
    acc 2 [];;
end


let () =
  let n = read_int () in
  (if n = 1 then "NO"
   else if FMath.is_prime n then "YES"
   else "NO") |> print_string;
  print_newline ();;