import Control.Applicative ((<$>))
import Data.Int (Int64)
import qualified Data.Vector.Unboxed as V

fibonacci :: (Integral a, V.Unbox a) => a -> a -> [a]
fibonacci a1 a2 = seq a1 $ a1 : fibonacci a2 (a1 + a2)

solve :: (Integral a, V.Unbox a) => a -> a -> Maybe a
solve n m = sol 0 (fromIntegral (n - 3)) d0
    where
        fibs = (V.fromList . take (fromIntegral n)) $ fibonacci 1 1
        d0 = V.last fibs - m
        sol a (-1) 0 = Just a
        sol _ (-1) _ = Nothing
        sol a i d
            | d >= f = sol (a + 1) (i - 1) (d - f)
            | otherwise = sol a (i - 1) d
            where f = fibs V.! i

main :: IO ()
main = do
    [n, m] <- fmap read . words <$> getLine :: IO [Int64]
    print $ case solve n m of
        Just a -> a
        Nothing -> -1