# coding: utf-8
N = int(input())
V = list(map(int, input().split()))
V.sort()
ans = 0
for i in range(N//2):
    tmp = (V[2*i] + V[2*i+1]) / 2
    if i == 0:
        ans = tmp
    else:
        ans = (ans + tmp) / 2
if N % 2 == 1:
    ans = (ans + V[-1]) / 2
print(ans)