#!/usr/local/bin/perl

# ----------------------------------------------------------------
# John Kerl
# kerl.john.r@gmail.com
# 2005-01-14
# ----------------------------------------------------------------

$psum = 0.0;
$n = 0;
while ($line = <>) {
	chomp $line;
	$n++;
	$line =~ s/^\s+//;
	$line =~ s/\s+$//;
	my @fields = split /\s+/, $line;
	if (@fields == 2) {
		$re = $fields[0];
		$im = $fields[1];
	}
	elsif (@fields == 1) {
		$re = $fields[0];
		$im = 0.0;
	}
	else {
		die "$0:  unrecognizable input at line $n.\n";
	}
	$pwr = $re*$re + $im*$im;
	$psum += $pwr;
}

$psum /= $n;
printf "%18.11f\n", $psum;