Score : $200$ points
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.
Input is given from Standard Input in the following format:
$N$ $S$
Print the largest possible number of different letters contained in both $X$ and $Y$.
6 aabbca
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 $2$.
10 aaaaaaaaaa
1
However we divide $S$, only a will be contained in both $X$ and $Y$.
45 tgxgdqkyjzhyputjjtllptdfxocrylqfqjynmfbfucbir
9