try:
    N = int(input())
    S = input()
    A = S.split()
    A = list(map(int, A))
    sum = [0]*(N)
    sum = A.copy()
    for k in range(0, N):
        for i in range(0, N-1):
            if((k+i)>=(N-1)):
                j = i+k+1-N
            else:
                j=i+k+1
            sum[k] = (sum[k]+A[j])/2
            
    print(max(sum))

except:
    print("Error")