/* 
 * This code is from "Algorithms in C, Third Edition,"
 * by Robert Sedgewick, Addison Wesley Longman, 1998.
 */
int puzzle(int N)
  {
    if (N == 1) return 1;
    if (N % 2 == 0)
         return puzzle(N/2);
    else return puzzle(3*N+1);
  }