t = gets.strip
s = gets.strip

s = s.split

for n in 0...s.length
    s[n] = s[n].to_i
end


while s.length > 1
    s = s.sort
    b = (s[0] + s[1])/2.to_f
    s.shift(2)
    s.push(b)
end


print s[0]