Problem:
Score : 200 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.
We will cut this string at one position into two strings X and Y.
Here, we would like to maximize the number of different letters contained in both X and Y.
Find the largest possible number of different letters contained in both X and Y when we cut the string at the optimal position.

Constraints

2 \leq N \leq 100

|S| = N

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the largest possible number of different letters contained in both X and Y.

Sample Input 1

6
aabbca

Sample Output 1

2

If we cut the string between the third and fourth letters into X = aab and Y = bca, the letters contained in both X and Y are a and b.
There will never be three or more different letters contained in both X and Y, so the answer is 2.

Sample Input 2

10
aaaaaaaaaa

Sample Output 2

1

However we divide S, only a will be contained in both X and Y.

Sample Input 3

45
tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir

Sample Output 3

9

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Arrow
import Data.Char
import Data.List

main :: IO ()
main = do
  _ <- getInt
  s <- getString
  print . maximum . map (length . uncurry intersect) . map (unique *** unique) $ zip (inits s) (tails s)

getInt :: IO Int
getInt = read <$> getLine

getString :: IO String
getString = getLine

unique :: Ord a => [a] -> [a]
unique = map head . group . sort