N = input()
a = input()
Ni = int(N)-1
l = a.split()
temp = 0
for i in range(int(len(l)+1)):
  for j in reversed(range(i, len(l))):
    if l[j-1]>l[j]:
      l[j-1],l[j] = l[j],l[j-1]

for i in range(int(Ni)):
  temp = (float(l[0])+float(l[1]))/2
  del l[:2]
  l.insert(1, temp)
  
print(temp)