n, k = map(int, input().split())
p = [int(i) for i in input().split()]
q = 0
for i in range(k):
  q += p[i]
r = q
for i in range(n - k):
  r -= p[i]
  r += p[i + k]
  if r > q:
    q = r
print((q + k) / 2) n, k = map(int, input().split()) n map(int, input().split()) map int input().split() ().split () input split k int(i) for i in input().split() for i in input().split() i input().split() ().split () input split for i in input().split() int(i) int i p = [int(i) for i in input().split()] p [int(i) for i in input().split()] q = 0 q 0 for i in range(k):
  q += p[i] i range(k) range k q += p[i] q p[i] p i r = q r q for i in range(n - k):
  r -= p[i]
  r += p[i + k]
  if r > q:
    q = r i range(n - k) range n - k n k r -= p[i] r p[i] p i r += p[i + k] r p[i + k] p i + k i k if r > q:
    q = r r > q r q q = r q r print((q + k) / 2) print (q + k) / 2 q + k q k 2 r += p[i + k] p[i + k] r r = q q r q = 0 0 q k = map(int, input().split()) map(int, input().split()) k q += p[i] p[i] q r -= p[i] p[i] r n, k = map(int, input().split()) map(int, input().split()) n q = r r q p = [int(i) for i in input().split()] [int(i) for i in input().split()] p
n, k = map(int, input().split())
p = [int(i) for i in input().split()]
q = 0
for i in range(k):
  q += p[i]
r = q
for i in range(n - k):
  r -= p[i]
  r += p[i + k]
  if r > q:
    q = r
print((q + k) / 2)