<?php

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


if ($n === 2) {
    $x = array_shift($m);
    $y = array_shift($m);
    $m[] = ($x + $y) / 2;
} else {
    while (count($m) > 1) {
        // 最小値
        $x = min($m);
        unset($m[array_search($x, $m)]);

        // その次の最小値
        $y = min($m);
        unset($m[array_search($y, $m)]);

        // 合成
        $z = ($x + $y) / 2;
        $m[] = $z;
    }
}

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