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;

namespace ConsoleApp11
{
    class Class31
    {
        static void Main()
        {
            int N = int.Parse(Console.ReadLine());
            string S = Console.ReadLine();
            List<char> I = new List<char>();
            List<char> K = new List<char>();
            int count = 0, countif = 0;
            for(int a = 1; a < S.Length-1; a++)
            {
                for (int i=0;i<a;i++)
                {
                    if (!I.Contains(S[i]))
                        I.Add(S[i]);

                }
                for(int k = a; k < S.Length; k++)
                {
                    if (!K.Contains(S[k]))
                        K.Add(S[k]);
                }
                for (int b = 0; b < K.Count(); b++)
                countif += I.Contains(K[b]) ? 1 : 0;
                count = Math.Max(count, countif);
                I.Clear();K.Clear();countif = 0;
            }
            Console.WriteLine(count);
        }
    }
}