
N = int(input())

A = list(map(int,input().split()))
A = sorted(A)
ans = 0
for i in range(N):
    if i == 0:
        ans += (A[i]+A[i+1])/2
        print(ans)
    elif i<N-1:
        ans = (ans+A[i+1])/2
print(ans)
