import Control.Applicative
import Control.Monad
import Data.Bits

rule :: [Int] -> (Int, Int)
rule x = (x !! 0, x !! 1)

hasEdge :: Int -> Int -> [(Int, Int)] -> Bool
hasEdge s v list = foldr edge False list
    where edge t b = b || (fst t) == v && testBit s (snd t)

func :: Int -> Int -> [(Int, Int)] -> Int
func s n t = if s == 1 then 1 else sum $ map (\a -> if (testBit s a) && not (hasEdge s a t) then func (clearBit s a) n t else 0) [1..n]

main :: IO ()
main = do
    [n, m] <- map read . words <$> getLine
    t <- replicateM m $ rule . map read . words <$> getLine
    let b = foldl (setBit) (bit 0) [1..n] :: Int

    putStrLn $ show $ func b n t

    return ()