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;

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

        var max = 0;
        for (int i = 1; i < s.Length; i++)
        {
            max = Math.Max(max, m1(s.Substring(0, i), s.Substring(i)));
        }
        Console.WriteLine(max);
    }

    static int m1(string x, string y)
    {
        var set = new HashSet<char>();
        var ans = 0;
        for (int i = 0; i < x.Length; i++)
        {
            if (set.Add(x[i]))
            {
                for (int j = 0; j < y.Length; j++)
                {
                    if (x[i] == y[j])
                    {
                        ans++;
                        break;
                    }
                }
            }
        }
        return ans;
    }
}