题解 | #字符个数统计#

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String line = scanner.nextLine();

        char[] charArray = line.toCharArray();

        List<String> list = new ArrayList<>();

        for (int i = charArray.length - 1; i >= 0 ; i--) {
            if (!list.contains(charArray[i] + ""))
                list.add(charArray[i] + "");
        }

        System.out.println(list.size());


    }
}