Using -n just complicates things for nothing.

With -n:

#!/usr/bin/perl -n

use strict;
use warnings;

our $total;

BEGIN {
   $total = 0;
}

$total += $_;

END {
   print $total, "\n";
}
[download]

Without -n:

#!/usr/bin/perl

use strict;
use warnings;

my $total = 0;

while ( <> ) {
   $total += $_;
}

print $total, "\n";
[download]

One is clearly a million times better.