<?php

$n = trim(fgets(STDIN));
$m = explode(' ', trim(fgets(STDIN)));

while (count($m) > 1) {
    sort($m);
    $x = array_shift($m);
    $y = array_shift($m);
    $m[] = ($x + $y) / 2;
}

echo current($m) . ".\n";