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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

var
  n,d,sln:int64;
  i:longint;
  j:char;
  s:ansistring;
BEGIN

  readln(n);
  read(s);

  sln:=low(int64);
  for i:=1 to n do
    begin
      d:=0;
      for j:='a' to 'z' do
        if (pos(j,copy(s,1,i))>0) and (pos(j,copy(s,i+1,n-i))>0) then
          d:=d+1;
      if sln<d then sln:=d;
    end;

  write(sln);

END.