function value = hail ( n )

%*****************************************************************************80
%
%% hail() computes the hail function.
%
%  Discussion:
%
%    Starting with a positive integer N, we divide it by 2 if it is
%    even, or triple and add 1 if odd, and repeat this process until
%    reaching the value 1.  The number of times the process is carried
%    out is the value of the hail function for the given starting value.
%
%    Actually, HAIL is not well defined, since it is not known if
%    the above process actually terminates at 1 for every starting value N.
%
%  Example:
%
%     N  Sequence                                                  Hail
%
%     1                                                               0
%     2   1                                                           1
%     3  10,  5, 16,  8,  4,  2,  1                                   7
%     4   2   1                                                       2
%     5  16,  8,  4,  2,  1                                           5
%     6   3, 10,  5, 16,  8,  4,  2,  1                               8
%     7  22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1   16
%     8   4,  2,  1                                                   3
%     9  28, 14,  7, ...                                             19
%    10   5, 16,  8,  4,  2,  1                                       6
%    11  34, 17, 52, 26, 13, 40, 20, 10,  5, 16, 8, 4, 2, 1          14
%    12   6,  3, 10,  5, 16,  8,  4,  2,  1                           9
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    26 July 2004
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    integer N, the starting value for the hail sequence.
%
%  Output:
%
%    integer VALUE, the number of steps before the hail sequence reached 1.
%
  k = 0;
  m = n;

  if ( 0 < n )

    while ( m ~= 1 )
      k = k + 1;
      if ( mod ( m, 2 ) == 0 )
        m = floor ( m / 2 );
      else
        m = 3 * m + 1;
      end
    end

  end

  value = k;

  return
end
