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 (3.8.2) (judge verdict: Accepted)

n = int(input())
s = input()
#n = 45
#s = "tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir"
ans = 0
alphabet = [chr(i) for i in range(97, 97+26)]
def count(i):
    num = 0
    a=list(set(list(s[:i])))
    b=list(set(list(s[i:])))
    for i in alphabet:
        if (i in a) & (i in b):
            num += 1
    return num
for j in range(1,len(s)-1):
    if ans < count(j): ans = count(j)
print(ans)