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 bla
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.ReadLine();
            string s = Console.ReadLine();
            int[] b = new int[26];
            int[] a = new int[26];
            for (int i = 0; i < s.Length; i++)
            {
                b[s[i] - 'a']++;
            }
            int max = 0;
            for (int i = 0; i < s.Length; i++)
            {
                max = Math.Max(max, count(a, b));
                b[s[i] - 'a']--;
                a[s[i] - 'a']++;
            }
            Console.WriteLine(max);
        }

        static int count(int[] a, int[] b)
        {
            int r = 0;
            for (int i = 0; i < 26; i++)
            {
                if(a[i] != 0 && b[i] != 0)
                {
                    r++;
                }
            }
            return r;
        }
    }
}