$ cat gen_targets.pl
#!/usr/bin/perl
use strict;
use warnings;
my $file = $ARGV[0] || 'targets.txt';
open (OUTPUT, '>', $file) or die "Unable to open $file for writing : $!";
print OUTPUT int rand 5_000_000, "\n" for 1 .. 5_000;

##</code><code>##

my $file = $ARGV[0] || 'targets.txt';
open (INPUT, '<', $file) or die "Unable to open $file for reading : $!";

while ( <INPUT> ) {
    chomp;
    get_three( $_ );  # used your sub/calling convention
}

##</code><code>##

$ time ./lr.pl

real    1m0.706s
user    1m0.416s
sys     0m0.080s

$ time ./fu.pl

real    1m0.791s
user    1m0.326s
sys     0m0.220s