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 8.8.3) (judge verdict: Accepted)

module Main where
 
import           Data.List
 
mapTuple :: (a -> b) -> (a, a) -> (b, b)
mapTuple f (a1, a2) = (f a1, f a2)
 
cut :: String -> Int
cut input = maximum $ map length leng
  where
    leng  = map (uncurry intersect . mapTuple nub) part
    part = map (`splitAt` input) [1..len]
    len  = length input
 
main :: IO()
main = interact $ show . cut . last . words