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 static System.Console;

class Program {
	static void Main() {
		var N = int.Parse(ReadLine());
		var S = ReadLine();
		var ans = 0;

		for (var i = 1; i < N; i++) {
			var a = S.Substring(0, i);
			var b = S.Substring(i);
			ans = Math.Max(ans, Calc(a, b));
		}
		WriteLine(ans);
	}

	static int Calc(string x, string y) {
		var result = 0;
		for (var c = 'a'; c <= 'z'; c++) {
			if (x.Contains(c + "") && y.Contains(c + "")) {
				result++;
			}
		}
		return result;
	}
}