$ time perl 892293.pl
Name "main::a" used only once: possible typo at 892293.pl line 21.
Name "main::b" used only once: possible typo at 892293.pl line 21.
Tails      Count     %
-----   ----------  ------
   0             1    0.00
   1            32    0.00
   2           496    0.00
   3          4960    0.00
   4         35960    0.00
   5        201376    0.00
   6        906192    0.02
   7       3365856    0.08
   8      10518300    0.24
   9      28048800    0.65
  10      64512240    1.50
  11     129024480    3.00
  12     225792840    5.26
  13     347373600    8.09
  14     471435600   10.98
  15     565722720   13.17
  16     601080390   13.99
  17     565722720   13.17
  18     471435600   10.98
  19     347373600    8.09
  20     225792840    5.26
  21     129024480    3.00
  22      64512240    1.50
  23      28048800    0.65
  24      10518300    0.24
  25       3365856    0.08
  26        906192    0.02
  27        201376    0.00
  28         35960    0.00
  29          4960    0.00
  30           496    0.00
  31            32    0.00
  32             1    0.00

real    0m0.034s
user    0m0.028s
sys     0m0.004s