import re

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

ans = (v[0]+v[1])/2

def del0(x):

    x = str(x)

    if re.search(r'\.0.+', x):
        return x
    
    elif re.search(r'\.0', x):
        x = x.replace(r'.0', '')
        return x
    else:
        return x

if n == 2:
    ans = ans
    print(del0(ans))

elif n > 2 and n % 2 == 0:
    for i in range(int(n/2)):
        ans = (ans + v[i+2])/2
    print(del0(ans))

elif n % 2 != 0:
    for i in range(n-2):
        ans = (ans + v[i+2])/2
    print(del0(ans))