<?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);

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

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

  }
}

#var_dump($nums);

$ans = round(array_sum($nums) / count($nums), 5);
  

echo $ans . PHP_EOL;



