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: Wrong Answer)

uses  crt;
var
        z:string;
        max,i,j,k,t:longint;
begin
        clrscr;
        read(z);
        writeln;
        for i:=1 to length(z)-1 do
                begin
                        t:=0;
                        for j:=1 to i do
                                for k:=i+1 to length(z) do
                                        if z[j]=z[k] then
                                                begin
                                                        inc(t);
                                                        break;
                                                end;
                        if t>max then max:=t;
                end;
        write(max);
        readln
end.