import itertools

N=int(input())
L=list(itertools.permutations(map(int,input().split())))
ANS=-1
for l in L:
  TMP = l[0]
  for i in range(1, N):
    TMP = (l[i] + TMP) / 2.0
  if ANS <= TMP:
    ANS = TMP
print(ANS)