Display Probability (FINAL)

Code
/// Name: Yordan Rashkov
/// Period: 7
/// Program Name: Display Probability
/// File Name: DisplayProbability.java
/// Date Finished: 1/21/2016

import java.util.Random;
import java.util.Scanner;

public class DisplayProbability
{
	public static void main( String[] args )
	{
		Scanner keyboard = new Scanner(System.in);
		Random r = new Random();
        int maximum, coin;
        double p1, amount, heads, tails, p2;
        heads = 0;
        tails = 0;
        amount = 0;
        maximum = 0;
        coin = r.nextInt(2);
        
        // It took me probably half of the period to figure out that I need to do double(s) and Int(s). I originally thought that I could go with String(s) and Int(s) because I copied the "flip again" program from the past. However that didn't work out so well. (LoL)
        
        do {
            System.out.println(" How many flips would you like?  :  ");
            maximum = keyboard.nextInt();
        }while ( maximum > 2100000000 && maximum < 1 );
        
        while (maximum < 2100000000 && maximum > 1 )
        {
            if ( coin == 1)
            {
            System.out.println(" Your flip turned out to be HEADS! ");
            amount = amount + 1;
            coin = r.nextInt(2);
            maximum = maximum - 1;
            heads = heads + 1;
            amount = amount + 1;
            }
            else if ( coin == 0 )
            {
            System.out.println(" Your flip turned out to be TAILS! ");
            amount = amount + 1;
            coin = r.nextInt(2);
            maximum = maximum - 1;
            tails = tails + 1;
            amount = amount + 1;
            }
        }
        
        // I decided to use while loops due to the fact that I have used them for the majority of the time. Do-while is also a good way to go here, except I'd like to keep it basic... While loops are pretty easy to remember how to do.
        
        p1 = heads / amount * 100;
        p2 = tails / amount * 100;
        System.out.println(" Your coin landed on heads " + heads + " time(s)... ");
        
        System.out.println(" Your coin landed on tails " + tails + " time(s)... ");
        
        System.out.println(" There is a " + p1 + " % chance that it landed on HEADS... ");
        
        System.out.println(" There is a " + p2 + " % chance that it landed on TAILS... ");
        
    }
}