N, K = map(int, input().split())
P = list(map(int, input().split()))

pos = 0
n = m = sum(P[0:K])
for i in range(1,N):
    if i+K > N:
        break
    n = n - P[i-1] + P[K-1+i]
    if n > m:
        pos = i
        m = n

print((sum(P[pos:pos+K]) + K) / 2) N, K = map(int, input().split()) N map(int, input().split()) map int input().split() ().split () input split K P = list(map(int, input().split())) P list(map(int, input().split())) list map(int, input().split()) map int input().split() ().split () input split pos = 0 pos 0 n = m = sum(P[0:K]) n sum(P[0:K]) sum P[0:K] P 0:K 0 K = m = sum(P[0:K]) m sum(P[0:K]) for i in range(1,N):
    if i+K > N:
        break
    n = n - P[i-1] + P[K-1+i]
    if n > m:
        pos = i
        m = n i range(1,N) range 1 N if i+K > N:
        break
     i+K > N i+K i K N break n = n - P[i-1] + P[K-1+i] n n - P[i-1] + P[K-1+i] n - P[i-1] n P[i-1] P i-1 i 1 P[K-1+i] P K-1+i K-1 K 1 i if n > m:
        pos = i
        m = n n > m n m pos = i pos i m = n m n print((sum(P[pos:pos+K]) + K) / 2) print (sum(P[pos:pos+K]) + K) / 2 sum(P[pos:pos+K]) + K sum(P[pos:pos+K]) sum P[pos:pos+K] P pos:pos+K pos pos+K pos K K 2 pos = 0 0 pos N, K = map(int, input().split()) map(int, input().split()) N P = list(map(int, input().split())) list(map(int, input().split())) P n = n - P[i-1] + P[K-1+i] n - P[i-1] + P[K-1+i] n pos = i i pos m = sum(P[0:K]) sum(P[0:K]) m n = m = sum(P[0:K]) sum(P[0:K]) n m = n n m K = map(int, input().split()) map(int, input().split()) K
N, K = map(int, input().split())
P = list(map(int, input().split()))

pos = 0
n = m = sum(P[0:K])
for i in range(1,N):
    if i+K > N:
        break
    n = n - P[i-1] + P[K-1+i]
    if n > m:
        pos = i
        m = n

print((sum(P[pos:pos+K]) + K) / 2)