import java.util.*;
public class TextBooks {

    public static void main(String[] args) {
        userInteraction();

    }
    public static void userInteraction(){
        q3();
    }


    public static void q3(){   //book cost
        Scanner userInput = new Scanner(System.in);
        double value =0;
        boolean test = false;
        int qNum = 3;


        while(true){
        System.out.println("What is the cost of the book?");
        try{
            value = Double.parseDouble(userInput.next());
            System.out.print(value);
            break;
        }catch (NumberFormatException e){
            System.out.println("Invalid input");
        }

    }
        //numValidation(qNum,valueTest);
    }}


        public static double numValidation(double x, String y){

            return numValue;


        }