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)

main = do
  n <- getLine
  s <- getLine
  putStrLn . show . solve $ s

solve :: String -> Int
solve s = maximum $ map (calc s) [1..(length s)]

calc s i = length $ filter (\c -> c `elem` (removeDup . (take i) $ s) && c `elem` (removeDup . (drop i) $ s)) ['a'..'z']

removeDup xs = helperRem [] xs
  where 
    helperRem seen [] = seen
    helperRem seen (x:xs) = if x `elem` seen then helperRem seen xs else helperRem (x:seen) xs