n,k = map(int,input().split())
array = list(map(int,input().split()))
for i in range(1,n):
	array[i] += array[i-1]

maxnumber = 0;
number = 0
while ( k <= n ):

	for i in range(n-k + 1):
		avg = 0;
		if i != 0:
			avg = array[ i + k - 1] - array[i-1]
		else:
			avg = array[ i + k - 1]

		avg = avg/k
		number = avg;
		if number > maxnumber:
			maxnumber = number;
	k+=1;
print ( maxnumber );