Conversion Program Works Except During First Try

It works everytime after the 1st choice is made. I was wondering why it doesn't work the first time though.
Output:
1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 1

1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 1
6.0 meters is 0.006 kilometers
1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 2
6.0 meters is 236.21999999999997 inches
1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 3
6.0 meters is 19.686 feet
1. Convert to kilometers
2. Convert to inches
3. Convert to feet
4. Quit the program

Enter your choice: 4
Bye
BUILD SUCCESSFUL (total time: 8 seconds)

import java.util.Scanner;

public class ConversionProgram
{
    public static void main(String[] args) 
    {
        menu();
    }
/////////////////////////////////////////////////////////////////
    public static void menu()
    {
        Scanner keyboard = new Scanner (System.in);
        System.out.print("Please enter a distance in meters: ");
        double meters = keyboard.nextDouble();
        
        System.out.println("1. Convert to kilometers");
        System.out.println("2. Convert to inches");
        System.out.println("3. Convert to feet");
        System.out.println("4. Quit the program");
        
        System.out.print("\nEnter your choice: ");
        int menu = keyboard.nextInt();
        
       while( menu != 4)
        {
        System.out.println("\n1. Convert to kilometers");
        System.out.println("2. Convert to inches");
        System.out.println("3. Convert to feet");
        System.out.println("4. Quit the program");
        
        System.out.print("\nEnter your choice: ");
        menu = keyboard.nextInt();
        
        
            if( menu == 1 )
            {
                showKilometers(meters);
            }
            else if( menu == 2 )
            {
                showInches(meters);    
            }
            else if( menu == 3 )
            {
                showFeet(meters);      
            }
            else if( menu == 4 )
            {
                System.out.println("Bye");
                exitProgram();
            }
        
        }
    }
/////////////////////////////////////////////////////////////////
    public static void showKilometers(double meters)
    {
        double kilometers;
        
        kilometers = meters * 0.001;
        System.out.print(+ meters + " meters is " + kilometers + " kilometers" );
    }
/////////////////////////////////////////////////////////////////
    public static void showInches(double meters)
    {
        double inches;
        
        inches = meters * 39.37;
        System.out.print(+ meters + " meters is " + inches + " inches" );
    }
/////////////////////////////////////////////////////////////////
    public static void showFeet(double meters)
    {
        double feet;
        
        feet = meters * 3.281;
        System.out.print(+ meters + " meters is " + feet + " feet" );
    }
/////////////////////////////////////////////////////////////////
    public static void exitProgram()
    {
        System.exit(0);   
    }
}