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.Linq;
using System.Collections.Generic;

    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string s = Console.ReadLine();

            int max = 0;
            int i = 0;
            int j = 0;

            for (i = 0; i < n; i++)
            {
                var leftList = new List<char>();
                var rightList = new List<char>();
                int count = 0;

                for (j = 0; j < i; j++)
                {
                    leftList.Add(s[j]);
                }
                for (j = i; j < n; j++)
                {
                    rightList.Add(s[j]);
                }
                leftList = leftList.Distinct().ToList();
                rightList = rightList.Distinct().ToList();
                foreach (char c in leftList)
                {
                    if (rightList.Exists(p => p == c))
                    {
                        count++;
                    }
                }
                max = max < count ? count : max;
            }

            Console.WriteLine(max);
        }
    }