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 PHP (5.6.30) (judge verdict: Wrong Answer)

<?php
fscanf(STDIN,'%d',$N);
fscanf(STDIN,'%s',$S);
$X='a';
$Y='a';
$A=[];
$B=[];
$c=0;
$max=0;
for ($i=1; $i <=$N-1 ; $i++) {
  // code...
  $X=substr($S,0,$i);
  $Y=substr($S,$i);
  $A=str_split($X);
  $B=str_split($Y);
  $c=0;
  for ($j=0; $j <count($A) ; $j++) {
    // code...
    if(in_array($A[$i],$B)){
      $c++;
    }
  }
  if($c>$max){
    $max=$c;
  }
}
echo $max;
echo "\n";
 ?>