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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;

public class Main {
	public static void main(String[] args) {
		int n = 0;
		String str = null;
		
		try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) {
			n = Integer.parseInt(br.readLine());
			str = br.readLine();
		} catch (IOException e) {
			return;
		}
		
		int max = 0;
		for (int i = 1; i < n - 1; i++) {
			String x = str.substring(0, i);
			String y = str.substring(i, n);
			
			int tmp = 0;
			if (x.length() < y.length()) {
				for (int j = 0; j < x.length(); j++) {
					if (x.indexOf(x.charAt(j)) == j &&
						y.indexOf(x.charAt(j)) >= 0) {
						tmp++;
					}
				}
			} else {
				for (int j = 0; j < y.length(); j++) {
					if (y.indexOf(y.charAt(j)) == j &&
					x.indexOf(y.charAt(j)) >= 0) {
						tmp++;
					}
				}
			}
			
			if (tmp > max) max = tmp;
		}
		
		System.out.println(max);
	}
}