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 Data.List
import Control.Monad

count :: Int -> String -> String -> Int
count acc [] ls = acc
count acc (x:xs) ls = if x `elem` ls then count (acc+1) xs ls' else count acc xs ls'
	where
		ls' = nub ls

main = do
	line <- fmap (\x -> read x :: Int) getLine
	str <- getLine
	counts <- forM [1..(line-1)] $ \x -> do
		let split = splitAt x str
		return $ count 0 (nub (fst split)) (snd split)
	putStrLn $ show $ maximum counts