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 AtCoder
{
	class Program
	{
		static void Main(string[] args)
		{
			var Instance = new Question();
			Instance.Exec();
		}
	}

	public class Question
	{
		public void Exec()
		{
			int n = int.Parse(Console.ReadLine());
			string dirs = Console.ReadLine();

			int max = 0;

			for (int i = 1; i < dirs.Length - 1; ++i) {
				string a = dirs.Substring(0, i);
				a = new string(a.Distinct().ToArray());
				string b = dirs.Substring(i, dirs.Length - i);
				b = new string(b.Distinct().ToArray());

				int count = 0;
				for (int j = 0; j < a.Length; ++j) {
					if (b.Contains(a[j])) {
						++count;
					}
				}

				if (max < count) {
					max = count;
				}
			}

			Console.WriteLine($"{max}");
			Console.ReadKey();
		}
	}
}