-- yukicoder My Practice
-- author: Leonardone @ NEETSDKASU

{-
    解説読後
    http://yukicoder.me/problems/875/editorial
    
    何人かの他の人のACコードを読んでみて解説の意味を理解した
-}

main = print . solve . map read . words =<< getLine

solve (n:m:_) = g rd dif 0 where 
    f = take n fib 
    rf = reverse f
    rd = drop 2 rf 
    fn = head rf
    dif = fn - m
    g []     d p    = if d == 0 then p else (-1)
    g (x:xs) d p
        | x > d     = g xs d       p
        | otherwise = g xs (d - x) (p + 1)

fib = [1, 1] ++ [(a + b) | x <- [0..], let (a:b:_) = drop x fib]