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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;

namespace ABC098_B_Cut_and_Count
{
	internal class Program
	{
		public static void Main(string[] args)
		{
			int n = int.Parse(Console.ReadLine());
			string s = Console.ReadLine();
			List<string> sSplit = new List<string>();
			
			for (int i = 0; i < n; i++) {
				sSplit.Add(s.Substring(i, 1));
			}

			int count = sSplit.Where(x => x == sSplit[0]).Count();
			string maxAppearStr = sSplit[0];

			for (int i = 1; i < n; i++)
			{
				int subCount = sSplit.Where(x => x == sSplit[i]).Count();
				if (subCount > count)
				{
					count = subCount;
					maxAppearStr = sSplit[i];
				}
			}
			
			Console.WriteLine(maxAppearStr);
		}
	}
}