Umnojenie po 2

import java.util.Scanner;

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

        double num = Double.parseDouble(scanner.nextLine()); //chislo i vuvejdane

        while(num>0){ // proverqva dali chisloto e positivno
            System.out.printf("%.2f", (num*2));
            num = Double.parseDouble(scanner.nextLine()); //otnovo vuvejdash chislo
        }
        System.out.println("Negative number!"); //sled kato e namerilo otricatelno - izpisva
    }
}