using System;

class RndBox {

  public RndBox()
  {
    random = new Random();
    available = false;
  }

  /* move to the next element of the pseudo random 
      sequence */

  public void Next() 
  {
    if (available)
      available = false;
    else
      generate();
  }
   
  /* pseudo random deviate from the gaussian 
      distribution */
 
  public double LastGaussian()
  {
    return available ? first : second;
  }

  // generate two pseudo random deviates from a 
  // gaussian distribution 

  private void generate()
  {
    randpoint();
    double p = Math.Sqrt((-2.0 * Math.Log(product)) / product);
    first = p * x;
    available = true;
    second = p * y;
  }

  // a point from a uniform distribution on the area 
  // of the unit circle 

  private void randpoint() 
  {
    do
    {
      x = randuniv() * 2 - 1;
      y = randuniv() * 2 - 1;
      product = x * x + y * y;
    } while (product > 1.0);
  }

  private double x, y, product, first, second;   
  private bool available;

  // internal wrapper for uniform distribution on 
  // unit interval 

  private double randuniv()
  {
    return random.NextDouble();
  }

  private Random random;
}