import Control.Monad
import Data.Maybe
import qualified Data.ByteString.Char8 as BS

readInt = fst . fromJust . BS.readInt
getInt = readInt <$> BS.getLine

main = do
    n <- getInt
    print $ solve n

solve n = check $ f n

check n | n `mod` 10 == 0 = 1 + check (n `div` 10)
        | n `mod` 10 /= 0 = 0

f 0 = 1
f 1 = 1
f n = n * f (n - 2)
