module Main where

import qualified Data.IntMap as M

main ::  IO ()
main = do size <- getLine
          nodes <- getLine
          let tree = map read . words $ nodes :: [Int]
              m = M.fromList $ map (\x -> (x, 1 + fun1 (a M.! x))) tree
              a = M.fromList $ zip [0 ..] tree
              fun1 (-1) = 1
              fun1 i = m M.! i
          print $ maximum $ map fun1 tree