@staticmethod
def c():
    (n, k, *r) = map(int, sys.stdin.read().split())
    print(reduce((lambda x, y: ((x + y) / 2)), sorted(r)[(- k):], 0))
@staticmethod
def c():
    (n, k, *r) = map(int, sys.stdin.read().split())
    print(reduce((lambda x, y: ((x + y) / 2)), sorted(r)[(- k):], 0))