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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

public class Hello
{
    public static void Main()
    {
        // Your code here!
        int N = int.Parse(Console.ReadLine());
        string S = Console.ReadLine();
        
        
        int max = 0;
        
       for(int i = 1;i <= S.Length; i++)  //文字列を2つの配列に分割
       {
          
           int sum = 0;
           string X = S.Substring(0, i);
           string Y = S.Substring(i);
           Dictionary<char, int> dic = new Dictionary<char, int>()
           {
               {'a',0},
               {'b',0},
               {'c',0},
               {'d',0},
               {'e',0},
               {'f',0},
               {'g',0},
               {'h',0},
               {'i',0},
               {'j',0},
               {'k',0},
               {'l',0},
               {'m',0},
               {'n',0},
               {'o',0},
               {'p',0},
               {'q',0},
               {'r',0},
               {'s',0},
               {'t',0},
               {'u',0},
               {'v',0},
               {'w',0},
               {'x',0},
               {'y',0},
               {'z',0},
               
            
           };
           
           List<char> idList = dic.Keys.ToList();
           foreach(var a in idList)
           {
               int indexX = X.IndexOf(a);
               int indexY = Y.IndexOf(a);
               if(indexX != -1 && indexY != -1)
               {
                   dic[a] += 1;
               }
           }
           foreach(var a in dic)
           {
               if(a.Value > 0)
               {
                   sum += 1;
               }
           }
           
           if(sum > max)
           {
               max = sum;
           }
           
           
           
       }
       Console.WriteLine(max);
       
    }
}