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,x,y:ansistring;
    i,j,k:longint;
    dem,l,o,a,b:int64;
begin
  readln(a);
  read(n);
  dem:=a;
  l:=low(int64);
  for k:=1 to a do
    begin
      dem:=0;
      x:=copy(n,1,k);
      y:=copy(n,k+1,a-k);
      for i:=1 to length(x)-1 do
        for j:=i+1 to length(x) do
          if x[i]=x[j] then x[j]:='0';
      for i:=1 to length(y)-1 do
        for j:=i+1 to length(y) do
          if y[i]=y[j] then y[j]:='1';
      for i:=1 to length(x) do
        for j:=1 to length(y) do if x[i]=y[j] then dem:=dem+1;
      if dem>l then l:=dem;;
    end;
  writeln(l);
  readln;
end.