While Loop to divide by 2 continiously

I'm working on a program that takes a number that is entered, then tells you how many times that number can be divided by 2 before it becomes less that 1. If a user enters a negative number it should tell the user that their input was invalid. This is what I have so far, but it isn't taking the count and increasing it every time. So what is wrong with my loop?

Code java:

package project6a;
 
import java.util.Scanner;
 
public class Bits {
 
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
 
		Scanner input = new Scanner (System.in);
 
		System.out.println("Enter a positive number: ");
		int userNumber = input.nextInt();
		int count = 0;
		int tempNum = userNumber / 2;
 
 
 
 
		while (tempNum >= 0){	
			tempNum = tempNum / 2;	
			count++;
 
			System.out.println("The number " + userNumber + " is divisible by two " + count + " times");
		}
 
		if (userNumber < 0)
			System.out.println("Invalid");	
 
 
		input.close();		
	}
}