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 ConsoleApp63 {
    class Program {
        static void Main(string[] args) {
            int N = int.Parse(Console.ReadLine());
            string S = Console.ReadLine();

            string zenhan = "";
            string kouhan = "";

            List<char> zen;
            List<char> kou;

            int ans = 0;

            for (int i = 1; i < N - 1; i++) {
                zenhan = S.Substring(0, i);
                kouhan = S.Substring(i, N - i);

                zen = zenhan.ToCharArray().ToList();
                kou = kouhan.ToCharArray().ToList();

                ans = Math.Max(ans, zen.Intersect(kou).Distinct().Count());


            }


            Console.WriteLine(ans);
        }

    }
}