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 Python (3.4.3) (judge verdict: Runtime Error)

#Cut and Count

#ライブラリ
import copy

#入力
N = int(input())
S = list(input())
ans = []
#計算
for j in range(1,N-1,1):
	counter = 0
	S_hidari = []
	S_migi = []
	S_hidari = set(copy.copy(S[0:j]))
	S_migi = set(copy.copy(S[j:N]))
	for s_hidari in S_hidari:
		for s_migi in S_migi:
			if s_hidari == s_migi:
				counter += 1
	ans.append(counter)

#出力
print(max(ans))