program Gray Code
// Input:    Integer n (0 - E) from standard input.
// Output:   Gray code of order n to standard output.
// -----------------------------------------------------------------------------

// Initialize
10: 8AFF   read RA                       n = StdIn.readInt()
11: 7101   R1 <- 1                       always 1
12: 5B1A   RB <- 1 << RA                 i = 2^n

                                         while (i != 0) {
13: 2BB1   RB <- RB - 1                     i = 2^n - 1
14: 6CB1   RC <- RB >> R1                   c = (i >> 1)
15: 4DBC   RD <- RB ^ RC                    d = i ^ (i >> 1)
16: 9DFF   write RD                         print RD
17: DB13   if (RB > 0) pc <- 13          }

18: 0000   halt