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 CSharpSample01
{


    class Program
    {


        static void Main(string[] args)
        {

            int N = int.Parse(Console.ReadLine());
            string S = Console.ReadLine();

            int ans = 0;

            for(int i = 1; i < N; i++)
            {
                var left = new Dictionary<char, int>();
                var right = new Dictionary<char, int>();
                int cnt = 0;

                for(int j = 0; j < i; j++)
                {
                    if (!left.ContainsKey(S[j])) left[S[j]] = 1;
                }
                for(int j = i; j < N; j++)
                {
                    if (!right.ContainsKey(S[j])) right[S[j]] = 1;
                }

                foreach(var s in left)
                {
                    if (right.ContainsKey(s.Key)) cnt++;
                }

                if (ans < cnt) ans = cnt;

            }

            Console.WriteLine(ans);

        }
    }
}