use strict;
use warnings;

sub predchar {
# modify argument in place.
# return true if no carry (done).
	my $ord= ord($_[0]);
	my $nocarry;
	# define the ranges available
	my @ranges= ([ord('a'),ord('z')], [ord('A'),ord('Z')] );
	foreach my $range (@ranges) {
		my ($first,$last)= @$range;
		next unless $ord >= $first && $ord <= $last;  # my range?
		if ($ord == $first) { $ord= $last; }
		else {
			$nocarry = 1;
			--$ord;
		}
	}
	$_[0]= chr($ord);
	return $nocarry;
}

sub magic_decrement($)
 {
	my $instr = $_;
	my $numpart = $instr;
	my $alphapart = $instr;
	$numpart =~ s/[A-Za-z]+//;
	$alphapart =~ s/[0-9]+//;
	my $numlen = length($numpart);
	$numpart--;
	if($alphapart) {
		 if($numpart == -1) {
			$numpart = '9' x $numlen;
			my @chars= split ('', $alphapart);
			my @retarr = @chars[0 .. $#chars];
			for (my $loop= $#chars;  $loop>=0;  --$loop) {
				last if predchar ($retarr[$loop]);
			}
			$alphapart = join ('',@retarr);
			$alphapart =~ s/[Zz]$// if($alphapart =~ /^[Zz]+$/);
		 } else {
			$numpart = '0' . $numpart if($numlen != length($numpart));
		 }
	}
	return $alphapart . $numpart;
 }

sub test
 {
 my $s= shift || $_;
 my $result= magic_decrement($s);
 my $reverse = $result;
 $reverse++;
 print qq{--"$s" gives "$result" reverse "$reverse"\n};
 }

while (<DATA>) { chomp; test; }

__DATA__
120
abc
testbaA
a
aaa
a01
aA00
Aa00
a00
0