<?php
ini_set('memory_limit', '1024M');

$n = trim(fgets(STDIN));
$vline = trim(fgets(STDIN));

$v = explode(' ', $vline);

if ((int) $n === 2) {
    echo ((double)$v[0] + (double)$v[1])/2;
    return;
}


$tmp = [];

for ($i = 0; $i < (int) $n; $i++) {
    $tmp[] = $v[$i];
}

$maxes = [];
divideTwoMax($tmp, $maxes);

echo max($maxes);

function divideTwoMax(array $arg, &$maxes) {



    foreach ($arg as $parentIndex => $item) {
        $arg2 = $arg;
        unset($arg2[$parentIndex]);
        foreach ($arg2 as $childIndex => $childItem) {

            if ($childIndex === $parentIndex) {
                continue;
            }

            unset($arg[$childIndex]);
            unset($arg[$parentIndex]);

            $res = $curr = ($item + $childItem) / 2.0;

            if (count($arg) < 1) {
                if (!in_array($res, $maxes)) {
                    $maxes[] = $res;
                }
                return;
            } else {
                $arg[] = $res;
                divideTwoMax($arg, $maxes);
            }

        }

    }

}