use strict;
use warnings;
$| = 1;

my $SAMPLE = 'AB ABDA DCACCB AAA BSAA CAAB ACS ABA DBA BA DASSABACA A';

local our $first;

$SAMPLE =~ m/
    (?: BA[ABC]{2} (?{ $first = 1; }) |
        CA[CD]{2}  (?{ $first = 2; }) |
        DA[SC]{2}  (?{ $first = 3; })
    ) /x;

print $first;


##</code><code>##

sub isNumber
{
  defined $_[0] or return 0;
  my $N = 1;
  local $SIG{__WARN__} = sub { $N = 0; };
  return ($_[0] & 0) | $N;
}