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: Accepted)

import collections
N = int(input())
S = input()
ans = 0
for i in range(1, N):
    left = S[:i]
    right = S[i:]
    count_left = collections.Counter(left)
    count_right = collections.Counter(right)
    count_left_unique = list(count_left.keys())
    count_right_unique = count_right.keys()
    cnt = 0
    for j in range(len(count_left_unique)):
        if(count_left_unique[j] in count_right_unique):
            cnt += 1
    ans = max(ans, cnt)
print(ans)