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;
using System.Text;
using System.Threading.Tasks;

namespace practice1
{
    class Program
    {
        static void Main(string[] args)
        {
            long number = long.Parse(MyScanf());
            string moziretsu = MyScanf();
            char[] c1, c2;
            c1 = new char[100];
            c2 = new char[100];
            int i, j, k, flag, count, max = 0;

            for (i = 1; i < moziretsu.Length; i++)
            {
                count = 0;
                c1 = moziretsu.ToCharArray(0, (int)i);
                c2 = moziretsu.ToCharArray(i, (moziretsu.Length - i));

                for (j = 0; j < c1.Length; j++)
                {
                    if (c1[j] == ' ') continue;
                    flag = 0;

                    for (k = 0; k < c2.Length; k++)
                    {
                        if (c1[j] == c2[k]) flag = 1;
                    }

                    if (flag == 1) count++;

                    for (k = 0; k < c2.Length; k++)
                    {
                        if (c1[j] == c2[k]) c2[k] = ' ';
                    }


                }

                if (count > max) max = count;
            }

            Println("" + max);

        }

        public static void Println(string str)
        {
            Console.WriteLine(str);
        }

        public static void Print(string str)
        {
            Console.Write(str);
        }

        public static string MyScanf()
        {
            return Console.ReadLine();
        }

        public static string[] MyScanfSplit()
        {
            return MyScanf().Split();
        }

        public static void MyDoubleSort(double[] boo)
        {
            if (boo.Length < 2) return;

            long i, count;
            double a;

            while (true)
            {
                count = 0;

                for (i = 0; i < boo.Length - 1; i++)
                {
                    if (boo[i] > boo[i + 1])
                    {
                        a = boo[i];
                        boo[i] = boo[i + 1];
                        boo[i + 1] = a;
                        count++;
                    }
                }

                if (count == 0) break;
            }
        }

        public static void MyLongSort(long[] boo)
        {
            if (boo.Length < 2) return;

            long i, count;
            long a;

            while (true)
            {
                count = 0;

                for (i = 0; i < boo.Length - 1; i++)
                {
                    if (boo[i] > boo[i + 1])
                    {
                        a = boo[i];
                        boo[i] = boo[i + 1];
                        boo[i + 1] = a;
                        count++;
                    }
                }

                if (count == 0) break;
            }
        }
    }
}