
N = int(input())
#s = input()
#S = []
#for i in range(N):
S = input().split(" ")
for i in range(N):
    S[i] = int(S[i])
for i in range(N-1):
    S[i+1] = (int(S[i])+int(S[i+1])) / 2
print(S[N-1])


