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: Wrong Answer)

N = int(input())
S = input()
mati = list()
maxi = 0
count = 0
for i in range(N):
  X = S[:i+1]
  Y = S[i+1:]
 
  for j in range(len(X)):
    for k in range(len(Y)): 
     
      if X[j] == Y[k]:
        if len(mati) == 0:
          mati.append(X[j])
        elif mati[len(mati)-1] == X[j]:
          mati.append(X[j])
        break
  if len(mati) >= maxi:
    maxi = len(mati)
    mati.clear()

print(maxi)