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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;

namespace ABC
{
    class ProgramB
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var s = Console.ReadLine();

            var result = 0;
            var max = s.Distinct().Count();
            for (var i = 1; i < n; i++)
            {
                var s1 = s.Substring(0, i).Distinct().ToArray();
                var s2 = s.Substring(i).Distinct().ToArray();
                var count = 0;
                for (var j = 0; j < s1.Length; j++)
                {
                    if (s2.Contains(s1[j]))
                    {
                        count++;
                    }
                }
                result = Math.Max(result, count);
            }

            Console.WriteLine(result);
        }
    }
}