n,k = map(int, input().split()) 

p = [int(x) for x in input().split()]
p_kitaiti=[float((x+1)/2) for x in p]

ruisekiwa=[p_kitaiti[0]]

for i in range(1,len(p_kitaiti)):
    ruisekiwa.append(ruisekiwa[-1]+p_kitaiti[i])

ans=ruisekiwa[k-1]

for i in range(1,len(ruisekiwa)-k+1):
    ans=max(ans,ruisekiwa[i+k-1]-ruisekiwa[i-1])

print(ans) n,k = map(int, input().split()) n map(int, input().split()) map int input().split() ().split () input split k int(x) for x in input().split() for x in input().split() x input().split() ().split () input split for x in input().split() int(x) int x p = [int(x) for x in input().split()] p [int(x) for x in input().split()] float((x+1)/2) for x in p for x in p x p for x in p float((x+1)/2) float (x+1)/2 x+1 x 1 2 p_kitaiti=[float((x+1)/2) for x in p] p_kitaiti [float((x+1)/2) for x in p] ruisekiwa=[p_kitaiti[0]] ruisekiwa [p_kitaiti[0]] p_kitaiti[0] p_kitaiti 0 for i in range(1,len(p_kitaiti)):
    ruisekiwa.append(ruisekiwa[-1]+p_kitaiti[i]) i range(1,len(p_kitaiti)) range 1 len(p_kitaiti) len p_kitaiti ruisekiwa.append(ruisekiwa[-1]+p_kitaiti[i]) ruisekiwa.append ruisekiwa append ruisekiwa[-1]+p_kitaiti[i] ruisekiwa[-1] ruisekiwa -1 p_kitaiti[i] p_kitaiti i ans=ruisekiwa[k-1] ans ruisekiwa[k-1] ruisekiwa k-1 k 1 for i in range(1,len(ruisekiwa)-k+1):
    ans=max(ans,ruisekiwa[i+k-1]-ruisekiwa[i-1]) i range(1,len(ruisekiwa)-k+1) range 1 len(ruisekiwa)-k+1 len(ruisekiwa)-k len(ruisekiwa) len ruisekiwa k 1 ans=max(ans,ruisekiwa[i+k-1]-ruisekiwa[i-1]) ans max(ans,ruisekiwa[i+k-1]-ruisekiwa[i-1]) max ans ruisekiwa[i+k-1]-ruisekiwa[i-1] ruisekiwa[i+k-1] ruisekiwa i+k-1 i+k i k 1 ruisekiwa[i-1] ruisekiwa i-1 i 1 print(ans) print ans p = [int(x) for x in input().split()] [int(x) for x in input().split()] p ans=max(ans,ruisekiwa[i+k-1]-ruisekiwa[i-1]) max(ans,ruisekiwa[i+k-1]-ruisekiwa[i-1]) ans k = map(int, input().split()) map(int, input().split()) k p_kitaiti=[float((x+1)/2) for x in p] [float((x+1)/2) for x in p] p_kitaiti n,k = map(int, input().split()) map(int, input().split()) n ruisekiwa=[p_kitaiti[0]] [p_kitaiti[0]] ruisekiwa ans=ruisekiwa[k-1] ruisekiwa[k-1] ans
n,k = map(int, input().split()) 

p = [int(x) for x in input().split()]
p_kitaiti=[float((x+1)/2) for x in p]

ruisekiwa=[p_kitaiti[0]]

for i in range(1,len(p_kitaiti)):
    ruisekiwa.append(ruisekiwa[-1]+p_kitaiti[i])

ans=ruisekiwa[k-1]

for i in range(1,len(ruisekiwa)-k+1):
    ans=max(ans,ruisekiwa[i+k-1]-ruisekiwa[i-1])

print(ans)