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 TestApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var str = Console.ReadLine();
            var lss = new List<int>();
            for (int i = 0; i <= n; i++)
            {
                var ls = str.ToList();
                var ls1 = new List<char>();
                var ls2 = new List<char>();

                var dic1 = new Dictionary<char, int>();
                var dic2 = new Dictionary<char, int>();


                for (int j = 0; j < i; j++)
                {
                    ls1.Add(ls[j]);
                }
                for (int k = i; k < n; k++)
                {
                    ls2.Add(ls[k]);
                }
                foreach (var item in ls1)
                {
                    if (!dic1.ContainsKey(item))
                        dic1.Add(item, 1);
                    else
                        dic1[item]++;
                }
                foreach (var item in ls2)
                {
                    if (!dic2.ContainsKey(item))
                        dic2.Add(item, 1);
                    else
                        dic2[item]++;
                }


                var ansDic = new Dictionary<char, int>();
                foreach (var item in dic1)
                {
                    if (dic2.ContainsKey(item.Key))
                        ansDic.Add(item.Key, dic2[item.Key] + item.Value);

                }
                lss.Add(ansDic.Count);
            }
            Console.WriteLine(lss.OrderByDescending(x => x).FirstOrDefault());
            Console.ReadLine();
        }
    }
}