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-----
6
aabbca

-----Sample Output-----
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.

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