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


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

solve (n:m:_) = g r df 0 where 
    f = take n fib 
    r = reverse f
    (fn,_) = last f
    df = fn - m
    g _          0 p = p
    g []         _ _ = (-1)
    g ((x,s):xs) d p
        | s < d     = (-1)
        | x > d     = g xs d p
        | otherwise = case ((g xs d p), (g xs (d - x) (p + 1))) of
            ((-1), b   ) -> b
            (a,    (-1)) -> a
            (a,    b   ) -> minimum [a, b]  
        

fib = [(1,1), (1,2)] ++ [(a + b, a + b + s) | x <- [0..], let ((a,_):(b,s):_) = drop x fib]