-- This is a parallel varient of factorial
 
 module Main where
 
 fac :: Int -> Int
 fac 0 = 1
 fac n = pfac 1 n
 
 pfac :: Int -> Int -> Int
 pfac low high | low == high     = low
               | low + 1 == high = (low * high)
               | otherwise       = pfac low mid * pfac (mid + 1) high
     where
        mid = (high + low) `div` 2
 
 main = appendChan stdout "Type in N: " abort $
        readChan stdin abort $ \ input ->
        appendChan stdout (show (fac (read (head (lines input))))) abort done