#!/usr/bin/env perl

use strict;
use warnings;

my $port = $ARGV[0];
my $used_ports = `netstat -tulan`;

my %p=();
my $addr=qr((?:\d+.\d+.\d+.\d+|[0-9a-f:]+));
for(split m/\R/, $used_ports) {
    if(m#$addr:(\d+)\s+$addr:(?:\d+|\*)\s+#) {
        $p{$1}=1;
    }
};

$port++ while $p{$port};

print $port