Кратность

import java.util.Scanner;

class Main{
    static int sigma;
    public static void main (String [] args){
        String input;
        Scanner reader = new Scanner (System.in);
        System.out.print("Введите число: ");
        input = reader.nextLine();
        char [] numbers = input.toCharArray();
        int check = 0;
        for (char number : numbers){
            if (number >= '0' && number <= '9'){
                check++;
            }
        }
        if (check == input.length()){
            Counter methods = new Counter();
            methods.worker(input);
        }
        else {
            System.out.print("Ошибка ввода!");
        }
    }
}

class Counter extends Main{
    void worker(String input){
        char [] number = input.toCharArray();
        for (char element : number){
            sigma += Integer.parseInt(String.valueOf(element));
        }
        if (sigma % 3 == 0){
            System.out.println("Кратно!");
        }
        else {
            System.out.println("Не кратно!");
        }
    }
}