use strict;
use warnings;

my %freq;

foreach my $file (@files) {
    open my $infh, '<', $file or die $!;
    while (<$infh>) {
        chomp;
        my ($freq, $data) = split /\s+/, $_;
        push @{$freq{$freq}}, $data;
    }
}

foreach my $k (sort {$a <=> $b} keys %freq) {
    print "$k @{$freq{$k}}\n";
}