N, K = map(int, input().split())
P = tuple(map(int, input().split()))
P2 = P[K:]

max_sum = 0
sum_ = sum(P[:K])

for p, q in zip(P, P2):
  max_sum = max(max_sum, sum_)
  sum_ += q - p
  
max_sum = max(max_sum, sum_)
          
res = (max_sum + K)/ 2
print(res) N, K = map(int, input().split()) N map(int, input().split()) map int input().split() ().split () input split K P = tuple(map(int, input().split())) P tuple(map(int, input().split())) tuple map(int, input().split()) map int input().split() ().split () input split P2 = P[K:] P2 P[K:] P K: K max_sum = 0 max_sum 0 sum_ = sum(P[:K]) sum_ sum(P[:K]) sum P[:K] P :K K for p, q in zip(P, P2):
  max_sum = max(max_sum, sum_)
  sum_ += q - p
   p q zip(P, P2) zip P P2 max_sum = max(max_sum, sum_) max_sum max(max_sum, sum_) max max_sum sum_ sum_ += q - p sum_ q - p q p max_sum = max(max_sum, sum_) max_sum max(max_sum, sum_) max max_sum sum_ res = (max_sum + K)/ 2 res (max_sum + K)/ 2 max_sum + K max_sum K 2 print(res) print res max_sum = 0 0 max_sum K = map(int, input().split()) map(int, input().split()) K P2 = P[K:] P[K:] P2 P = tuple(map(int, input().split())) tuple(map(int, input().split())) P N, K = map(int, input().split()) map(int, input().split()) N sum_ += q - p q - p sum_ max_sum = max(max_sum, sum_) max(max_sum, sum_) max_sum res = (max_sum + K)/ 2 (max_sum + K)/ 2 res sum_ = sum(P[:K]) sum(P[:K]) sum_ max_sum = max(max_sum, sum_) max(max_sum, sum_) max_sum
N, K = map(int, input().split())
P = tuple(map(int, input().split()))
P2 = P[K:]

max_sum = 0
sum_ = sum(P[:K])

for p, q in zip(P, P2):
  max_sum = max(max_sum, sum_)
  sum_ += q - p
  
max_sum = max(max_sum, sum_)
          
res = (max_sum + K)/ 2
print(res)