N, K = map(int, input().split())
nums = list(map(int, input().split()))
expect = 0
answer = 0
for i in range(N):
  if i < K:
    expect += (nums[i]+1)/2
  else:
    expect += (nums[i]+1)/2 - (nums[i-K]+1)/2
  answer = max(answer, expect)
print(answer) N, K = map(int, input().split()) N map(int, input().split()) map int input().split() ().split () input split K nums = list(map(int, input().split())) nums list(map(int, input().split())) list map(int, input().split()) map int input().split() ().split () input split expect = 0 expect 0 answer = 0 answer 0 for i in range(N):
  if i < K:
    expect += (nums[i]+1)/2
  else:
    expect += (nums[i]+1)/2 - (nums[i-K]+1)/2
  answer = max(answer, expect) i range(N) range N if i < K:
    expect += (nums[i]+1)/2
  else:
    expect += (nums[i]+1)/2 - (nums[i-K]+1)/2
   i < K i K expect += (nums[i]+1)/2 expect (nums[i]+1)/2 nums[i]+1 nums[i] nums i 1 2 expect += (nums[i]+1)/2 - (nums[i-K]+1)/2 expect (nums[i]+1)/2 - (nums[i-K]+1)/2 (nums[i]+1)/2 nums[i]+1 nums[i] nums i 1 2 (nums[i-K]+1)/2 nums[i-K]+1 nums[i-K] nums i-K i K 1 2 answer = max(answer, expect) answer max(answer, expect) max answer expect print(answer) print answer K = map(int, input().split()) map(int, input().split()) K nums = list(map(int, input().split())) list(map(int, input().split())) nums expect += (nums[i]+1)/2 - (nums[i-K]+1)/2 (nums[i]+1)/2 - (nums[i-K]+1)/2 expect answer = max(answer, expect) max(answer, expect) answer expect = 0 0 expect expect += (nums[i]+1)/2 (nums[i]+1)/2 expect N, K = map(int, input().split()) map(int, input().split()) N answer = 0 0 answer
N, K = map(int, input().split())
nums = list(map(int, input().split()))
expect = 0
answer = 0
for i in range(N):
  if i < K:
    expect += (nums[i]+1)/2
  else:
    expect += (nums[i]+1)/2 - (nums[i-K]+1)/2
  answer = max(answer, expect)
print(answer)