(JAVA) Make a loop were a random value changes every time the loop restarts

I am making a coin flip simulator, but I have a problem with the random values. I need to make a random value that changes every time the while-loop starts again.

    System.out.println("How many times do I flip the coin?");
    int repetition;
    int heads = 0;
    int tails = 0;
        Scanner amount_of_times = new Scanner(System.in);
    repetition = amount_of_times.nextInt();
    double luck = (Math.random());
    do {
        if (luck > 0.5)
            heads++ ;
        else
            tails++ ;
        repetition --;
    } while (repetition > 0);
    System.out.println("The amount of heads was " + heads + ", meanwhile the amount of tails was " + tails + ".");
        amount_of_times.close();
    }
}