<?php

fscanf(STDIN, "%s", $count);
$source = fgets(STDIN);
$matterials = explode(" ", $source);
sort($matterials);

for ($i=0; $i < $count - 1; $i++)
{
	$$matterials[$i] = ($matterials[$i] + $matterials[$i+1])/2;
}

print($matterials[$count-1]);