my $N =  <STDIN>;
chomp ($N);
my @A;
foreach (split(/ /o, <STDIN>)) {
  chomp($_);
  push(@A, $_) if ($_ ne '');
}
my $i = 0;
my $t = 0;
my $k = 1;
foreach my $a (sort @A) {
  if ($i == 0) {
    $t += $a;
  } else {
    $t += $k*$a;
    $k = $k * 2;
  }
  $i++;
}
print $t/$k;