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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
$n = trim(fgets(STDIN));
$str = trim(fgets(STDIN));

$maxSize = 0;
for($i = 0; $i < $n; $i++){
    $map1 = $map2 = [];
    for($j = 0; $j < $n; $j++){
        if($i < $j){
            $map1[$str[$j]] = true;
        }else{
            $map2[$str[$j]] = true;
        }
    }
    $size = count(array_intersect(array_keys($map1), array_keys($map2)));
    $maxSize = max($size, $maxSize);
}
echo $maxSize;