Final Exam: Coin Flip w/ Probability

Code

    /// Name: Cassie
    /// Period: 6
    /// Program Name: Final Exam
    /// File Name: finalExam.java
    /// Date Finished: 1/22/2016
    
    import java.util.Random;
    import java.util.Scanner;
    
    class finalExam
    {
    	public static void main( String[] args )
    	{            
    		Scanner keyboard = new Scanner(System.in);
            Random rng = new Random();
    
            int flipAmount; 
            int tries = 0, heads = 0, tails = 0;
            
            System.out.println( "Pick an amount of times to flip the coin" );
            System.out.println( "(No less than one no greater than 2,100,000,000)" );
            System.out.print( " >  " );
            flipAmount = keyboard.nextInt();
            
            if ( flipAmount > 2100000000 )
            {
                System.out.println( "That number does not follow the guidelines" );
                System.out.println( "Select a new number that is no less than one no greater than 2,100,000,000" );
                System.out.print( " >  " );
                flipAmount = keyboard.nextInt();
            }
            
            if ( flipAmount < 1 )
            {
                System.out.println( "That number does not follow the guidelines" );
                System.out.println( "Select a new number that is no less than one no greater than 2,100,000,000" );
                System.out.print( " >  " );
                flipAmount = keyboard.nextInt();
            }
            
            do
        		{
        			int flip = rng.nextInt(2);
                    tries ++;
        
        			if ( flip == 1 )
        				heads++;
        			else
        				tails++;            
                } while ( tries < flipAmount);
            System.out.println( "You rolled " + heads + " heads and " + tails + " tails." );
            
            double probabilityOfHeads = heads++ / flipAmount;
            double probOfHeads = (((double)heads++) / flipAmount) * 100;
            System.out.println( "Your probability of rolling heads is " + probOfHeads );
        }   
    }
    

Picture of the output