import itertools

n = int(input())
foods = [int(i) for i in input().split()]

#print(list(itertools.permutations(foods)))
result_value = []
for i in list(itertools.permutations(foods)):

    temp_value = i[0]
    for j in range(1,len(i)):
        temp_value = (temp_value + i[j])/2
    result_value.append(temp_value)

#print(sorted(result_value))
result_value = sorted(result_value,reverse=True)

print(result_value[0])

