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;
public class Program
{
	static void Main(string[] args)
	{
		int n = int.Parse(Console.ReadLine());
		string s = Console.ReadLine();


		
		int max = 0;
		for (int i = 1; i < n; i++)
		{
			var ldic = new Dictionary<char, bool>();
			for (int k = 0; k < 26; k++)
			{
				ldic[Convert.ToChar(97 + k)] = false;
			}
			var rdic = new Dictionary<char, bool>(ldic);

			for (int j = 0; j < i; j++)
			{
				ldic[s[j]] = true;
			}
			for (int j = i; j < n; j++)
			{
				rdic[s[j]] = true;
			}
			
			int count = System.Linq.Enumerable
							.Range(97, 26)
							.Count(e => ldic[Convert.ToChar(e)] == true && rdic[Convert.ToChar(e)] == true);

			if (count > max)
			{
				max = count;
			}
		}
		Console.WriteLine(max);
	}
}