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 PyPy3 (7.3.0) (judge verdict: Runtime Error)

N=int(input())
S=input()
A=[]
for i in range(1,N):
    A.append([list(S[:i]),list(S[i:])])
for i in range(N-1):
    for j in range(1,len(A[i][0])):
        for k in range(1,len(A[i][0])):
            if j<k and A[i][0][j-1]==A[i][0][k-1]:
                A[i][0].remove(A[i][0][k-1])
B=[]
for i in range(N-1):
    B.append(0)
for i in range(N-1):
    for j in range(len(A[i][0])):
        B[i]+=A[i][1].count(A[i][0][j])
print(max(B))