<?php

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

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

    // 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";