import qualified Data.Set as S
import Data.Array
import Data.List
main = do
  n <- readLn
  a <- map read . words <$> getLine :: IO [Int]
  let g = accumArray (flip (:)) [] (0, n) $ zip a [1..]
      dfs s i x = foldl' (\y j -> dfs (S.insert j s) j y) (S.findIndex i s + x) (g ! i)
  print $ dfs (S.singleton 0) 0 0