n=int(input())
v=list(map(int, input().split()))

v.sort()
dif=[v[i+1]-v[i] for i in range(n-1)]

while len(v)>2:
  i=dif.index(min(dif))
  v[i]=(v[i]+v.pop(i+1))/2
  dif.pop(i)
  dif[i]=v[i+1]-v[i]
  if i!=0: dif[i-1]=v[i]-v[i-1]

print((v[0]+v[1])/2)  