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 Perl (v5.18.2) (judge verdict: Wrong Answer)

$line = <STDIN>;
chomp $line;
$N=scalar($line);
$line = <STDIN>;
chomp $line;
$S=$line;

$mm=-1;$mi=-1;$m=0;

for($i=0;$i<$N;$i++){
	$k=substr($S,$i,1);
	$ri=rindex($S,$k,$i-1);
	$li=index($S,$k,$i+1);
	if ($li>=0) {
		if($ri>=0) {
			#no change
		} else {
			$m+=1;
			if($mm<$m) {
				$mm=$m;
				$mi=$i;
			}
		}
	} else {
		if($ri>=0) {
			$m-=1;
		} else {
			#no change
		}
	}
}

print "$mm\n";