try:
    N = int(input())
    S = input()
    A = S.split()
    A = list(map(float, A))
    sum1 = (A[0]+A[1])/2
    for i in range(0,N-2):
     sum1 = (sum1 + A[i+1])/2

    print(sum1)

except:
    print("Error")