1  int x, y;
       2  
       3  int
       4  main()
       5  {
       6    x = 2;
       7    y = x;
       8    do
       9      {
      10        x = y;
      11        y = 2 * y;
      12      }
      13    while ( ! ((y - x) >= 20));
      14    exit (0);
      15  }
      16