Assignemnt Final Exam Coin Flip Probability

Code

    ///Name: Joshua Pell
    ///Period: 6
    ///Project Name: Final Exam
    ///File Name: FinalExam.java
    ///Date: 1/22/2015
    
 import java.util.Random;
import java.util.Scanner;
    
    public class FinalExam
    {
        public static void main(String[] args) 
        {
            Scanner key = new Scanner(System.in);
            Random r = new Random();
            int d1;
            int heads = 0,tails = 0, flips;
            
            System.out.println("How many times do you want to flip the coin?");
            flips = key.nextInt();
            int rflips = flips;
            if (flips < 1 ||flips >2100000000)
            System.out.println("Invalid. Please Enter New Number");
            else
            {
            while (rflips>0)
                {
                    d1 = r.nextInt(2);
                    if (d1==1)
                    {
                        heads++;
                    }
                    else
                    {
                        tails++;
                    }
                    rflips= rflips-1;
                }
            }
            
            System.out.println("You flipped "+heads+" heads and "+tails+" tails");
            double pheads = (double)heads / flips;
            System.out.println("The probability you flipped heads is "+pheads);
            double ptails = (double)tails / flips;
            System.out.println("The probability you flipped tails is "+ptails);
            //To get as close as possible to 50% it would be best to do 2,100,000,000 flips
        }
    }
    

Picture of the output