try:
    N = int(input())
    if N>1:
        S = input()
        A = S.split()
        A = list(map(int, A))
        if all(i > 0 or i < 1000 for i in 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")