n = int(input())
cnt = 0

while True:
    if n == 2:
            break
    else:
        if n % 2 == 0:
            n = n // 2
            cnt += 1
        else:
            n = n // 2 + 1
            cnt += 1

l = [[] for _ in range(cnt+1)]
l[0] = list(map(int, input().split()))
l[0].sort()


for i in range(cnt):
    for j in range(0,n,2):
        l[i+1].append((l[i][j] + l[i][j+1]) / 2)
        if n // 2 == 1:
            l[i+1].append(l[i][n])

print((l[cnt][0] + l[cnt][1]) / 2)