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 = str(input())
types = []
for i in range(len(s)-1):
    x = s[:i]
    y = s[i:]
    x.sort()
    y.sort()
    x_str = []
    y_str = []
    x_str.append(x[0])
    y_str.append(y[0])
    count = 0
    for i in range(1,len(x)):
        if x[i-1] != x[i]:
            x_str.append(x[i])
    for i in range(1,len(y)):
        if y[i-1] != y[i]:
            y_str.append(y[i])
    for i in range(len(x_str)):
        if x_str[i] in y_str:
            count += 1
    types.append(count)
print(max(types))