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