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)

def func(s1, s2):
    set1 = set(s1)
    set2 = set(s2)

    cnt = 0
    for _ in range(len(set1)):
        s = set1.pop()
        if s in set2:
            cnt += 1
    return cnt


def main():
    n = int(input())
    s = input()

    mx = 0
    for i in range(len(s) - 1):
        s1 = s[:i + 1]
        s2 = s[i + 1:]
        ans = func(s1, s2)
        if ans > mx:
            mx = ans

    print(mx)


if __name__ == '__main__':
    main()
    # print(func([1, 2, 2, 3], [2, 3, 4, 4, 1]))