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)

n = int(input())
s = input()
ls = []

for i in range(1,n-1):
  
  dic_f = {}
  dic_l = {}
  former = s[:i]
  latter = s[i+1:]
  counter = 0
  
  for j in range(len(former)):
    if former[j] not in dic_f.keys():
      dic_f[former[j]] = 1
      
  for j in range(len(latter)):
    if latter[j] not in dic_l.keys():
      dic_l[latter[j]] = 1
      
  for j in dic_f.keys():
    if j in dic_l.keys():
      counter += 1
  ls.append(counter)

print(max(ls))