#!/usr/bin/perl -w
$sum=0;
$count=0;

open(INPUT,"meres.txt") or die "ERROR";
while($line=<INPUT>)

{
	chomp($line);
	if($line=~/([-\d]+(\d+)*)/){
		#print($1."\n");
		$sum+=$1;
		$count++;
	}
}
close(INPUT);
print $sum/$count;
print "\n";