module Main where

import Control.Monad

to10 :: Int -> Int
to10 x = (1 * x ^ 1) + (7 * x ^ 0)

main :: IO ()
main = do
    a <- readLn :: IO Int
    let bs = filter ((== a) . to10) $ [2 .. 100]
    if null bs
        then print (-1)
        else print $ head bs