<?php
  
while ($line = fgets(STDIN)) {
   $stdin[] = trim($line);
}
#$v2 = str_split($stdin[0]);
#$v2 = explode(" ", $stdin[0]);

$nums = explode(" ", $stdin[1]);

$max = max($nums);

sort($nums);

#var_dump($nums);

#誤差？対策
foreach($nums as $v){
  $nums2[] = $v * 100000000;
}

#var_dump($nums2);

if(count($nums2) == 2){
  $ans = array_sum($nums) / count($nums);
}else{
  
  for($i = 0; $i <= count($nums2); $i++){

    $temp = ($nums2[$i] + $nums2[$i + 1]) / 2;
    unset($nums2[$i]);
    $nums2[$i + 1] = $temp;

  }
  
  #var_dump($nums2);
  
  $ans = (array_sum($nums2) / count($nums2)) / 100000000;
}

  

echo $ans . PHP_EOL;



