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;

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

            var maxV = 0;
            for(var i = 1; i < n; i++){
                var x = s.Substring(0, i);
                var y = s.Substring(i, n - i);

                var d = new Dictionary<char,int>();
                foreach(var c in x){
                    if(!d.ContainsKey(c)){
                        d.Add(c, 1);
                    }
                }
                foreach(var c in y){
                    if(d.ContainsKey(c)){
                        d[c] += 1;
                    }
                }

                var count = d.Where(t => t.Value >= 2).Count();
                maxV = Math.Max(maxV, count);
            }

            Console.WriteLine(maxV);
        }
    }
}