#!/usr/bin/perl

# Copyright 2001 John Ackermann   Version: 15 July 2001
# May be freely used provided these notices are retained, and a copy
# of any modified version that's distributed to third persons is sent
# to jra@febo.com

$count = 1;
$runtotal = 0;
while ($reading=<STDIN>) {
	$runtotal += $reading;
	$count++;
};
printf "%+10.8e", $runtotal/$count;