{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE ExplicitForAll #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE Unsafe #-}
{-# LANGUAGE RecordWildCards #-}

import Data.Bits
import Data.List
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.Lazy.Char8 as BSL
import Data.IntMap.Strict (IntMap)
import qualified Data.IntMap.Strict as IMS
import Data.IntSet (IntSet)
import qualified Data.IntSet as IS
import qualified Data.Array.IArray as A
import qualified Data.Array.MArray.Safe as A
-- import qualified Data.Array.MArray as A
import Data.Array (Array)
import Data.Array.Unboxed (UArray)
import Data.Array.IArray (IArray)
import Data.Array.MArray.Safe (MArray)
import Data.Array.IO.Safe (IOArray, IOUArray)
import Data.Array.ST.Safe (STArray, STUArray, runSTArray, runSTUArray)
import qualified Data.Vector as V
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import Control.Monad
import Control.Monad.ST
-- import Control.Monad.ST.Safe
import Control.Applicative
import Data.Maybe
import Data.Tuple
import Data.Ord
import Control.Monad.State.Strict
import Data.Int
import System.IO
import Data.Function


main :: IO ()
main = do
  n <- read <$> getLine
  ls <- VU.unfoldrN n (BS.readInt . BS.dropWhile (==' ')) <$> BS.getLine
  print $ binSearch 0 n ls

binSearch :: Int -> Int -> VU.Vector Int -> Int
binSearch ng ok ls | ok - ng <= 1 = ok
binSearch ng ok ls =
  if isPossibleWith mid ls then
    binSearch ng mid ls
  else
    binSearch mid ok ls
  where
    mid = (ng + ok) `shiftR` 1


isPossibleWith :: Int -> VU.Vector Int -> Bool
isPossibleWith 1 ls = VU.and $ VU.zipWith (<) ls (VU.tail ls)
isPossibleWith numChars ls
  = VU.foldr loop (const True) ls (DicEntry 0 Nil)
  where
    loop !reqLen cont de@DicEntry{..}
      | reqLen > wordLen = cont $! de{wordLen = reqLen}
      | otherwise = loop1 ((cont $!) . DicEntry reqLen)
                    (cutOff charList reqLen) (reqLen - 1)
    loop1 _ !xs ind | ind < 0 = False
    loop1 cont xs@(Snoc xs' i e) ind = case compare i ind of
      LT -> cont $! Snoc xs ind 1
      EQ | e < numChars - 1 -> cont $! Snoc xs' i (e+1)
         | otherwise        -> loop1 cont xs' (ind-1)
    loop1 cont Nil ind = cont $! Snoc Nil ind 1

data List = Nil | Snoc !List {-# UNPACK #-} !Int {-# UNPACK #-} !Int
 deriving Show

data DicEntry = DicEntry { wordLen :: {-# UNPACK #-} !Int,
                           charList :: !List }

cutOff :: List -> Int -> List
cutOff (Snoc xs i e) till | till <= i = cutOff xs till
cutOff xs !till = xs
