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;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var S = Console.ReadLine();
            int maxTypes = 0;

            for (int i = 1; i < N; i++)
            {
                int maxCount = 0;

                var X = S.Substring(0, i);
                var Y = S.Substring(i, N - i);

                for(int j = 0; j < X.Length; j++)
                {
                    bool Xcontain = false;

                    for(int k = 0; k < j; k++)
                    {
                        if (X.Substring(j, 1) == X.Substring(k, 1)) Xcontain = true;
                    }
                    if (Xcontain) continue;

                    for(int k = 0; k < Y.Length; k++)
                    {
                        if (X.Substring(j, 1) == Y.Substring(k, 1))
                        {
                            maxCount++;
                            break;
                        }
                    }
                }

                if (maxCount > maxTypes) maxTypes = maxCount;
            }

            Console.WriteLine(maxTypes);
        }    
    }
}