import random
element, repeat = map(int, input().split())
numbers = []
for ele in element:
    numbers.append(ele)
    
def add_number(choice, num):
    return num + choice

sum_numbers = []
for _ in repeat:
    for number in numbers:
        add_numbers = list(map(add_numbers(number, numbers)))
        sum_numbers.append(sum(add_numbers))

print(sum(sum_numbers) / element)