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

namespace MyProgram
{
    public class Program
    {	
        public static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string s = Console.ReadLine();
            
            int max = 0;
            string s1 = "";
            string s2 = "";
            
            int cnt = 0;
            for(int i = 1 ; i < s.Length ; i++)
            {
                s1 = s.Substring(0,i);
                s2 = s.Substring(i,n-i);
                cnt = 0;
                
                for(int j = 0 ; j < 26 ; j++)
                {
                    char c = (char)('a'+j);
                    if(s1.Contains(c) && s2.Contains(c)) cnt++;
                }
                max = Math.Max(max,cnt);
            }
            Console.WriteLine(max);
        }
    }
}