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)

n = int(input())
s = input()
t = list(s)

s1 = []
s2 = []

for i in range(n):
  s1.append([])
  s2.append([])

for i in range(n):
  for j in range(n):
    if j < i:
      s1[i].append(t[j])
    else:
      s2[i].append(t[j])

count = 0
com = []
slv = []
      
for i in range(n):
  for j in range(i):
    if s1[i][j] in s2[i] and s1[i][j] not in com:
      count += 1
      com.append(s1[i][j])
  slv.append(count)
  count = 0
  com = []
  
print(max(slv))