use strict;
use warnings;

my @files = grep /^output\d+$/, <output*>;
my ( $total, $i );
foreach my $file (@files) {
    open ( my $in, "<$file" ) or die "Couldn't open $file: $!\n";
    while ( my $input = <$in>) {
        print "$file\n";
        my ($x, $y, $z, $sum) = split (/\s+/, $input);
        $total += $sum;
        $i++;
        my $div = $total/$i;
        my $sqrt = sqrt($div);
        print "$total\n";
        open ( my $out2, ">RMSD$file") 
            or die "Couldn't open RMSD$file: $!\n";
        print $out2 $sqrt;
        close $out2;
    }
    close $in;
}