use warnings;
use strict;

sub A
 {
 return 0  if $_[1] == 0; 
 return 2*$_[1]  if $_[0] == 0;
 return 2  if $_[1] == 1;
 # figure A(m-1, A(m, n-1)) using in-place parameter list to save stack.
 --$_[1];
 $_[1]= &A;
 --$_[0];
 return &A;
 }

print A ($ARGV[0], $ARGV[1]);