use warnings;
use strict;

use Data::Dumper;

my @files = <DATA>;
chomp @files;

warn Dumper \@files;

sub get_least($) {
    my $md5 = shift;

    my $num = (
        sort map { s/${md5}_//; s/_max//; ($_) } grep /^$md5.*_max/, @files
    )[0];

    warn("No max file"), return undef unless $num;
    return $num;
}

warn get_least(q/111aaa222ccc324567fed54333221235/);
warn get_least(q/777aaa222ccc324567fed54333221235/);
warn get_least(q/99999999999999999999999999999999/);

__DATA__
111aaa222ccc324567fed54333221235_1.04
111aaa222ccc324567fed54333221235_1.05_max
111aaa222ccc324567fed54333221235_0.98_min
111aaa222ccc324567fed54333221235_1.02_max
111aaa222ccc324567fed54333221235_0.21
777aaa222ccc324567fed54333221235_1.04
777aaa222ccc324567fed54333221235_1.07_min
777aaa222ccc324567fed54333221235_1.04_max
99999999999999999999999999999999_1.04
99999999999999999999999999999999_1.07_min
99999999999999999999999999999999_1.04_min