1 #include <cstdio>
 2 #include <cstring>
 3 #define N 300010
 4 using namespace std;
 5 int n,k;
 6 double l,r,mid,a[N],b[N],eps=1e-5;
 7 bool check(int x)
 8 {
 9     double p=0;
10     for (int i=k;i<=n;i++)
11     {
12         if (b[i]-p>=0) return 1;
13         if (b[i-k+1]<p) p=b[i-k+1];
14     }
15     return 0;
16 }
17 int main()
18 {
19     freopen("average.in","r",stdin),freopen("average.out","w",stdout),scanf("%d%d",&n,&k);
20     for (int i=1;i<=n;i++) scanf("%lf",&a[i]),r+=a[i];
21     while (r-l>eps)
22     {
23         double mid=(l+r)/2.0; b[0]=0;
24         for (int i=1;i<=n;i++) a[i]-=mid,b[i]=b[i-1]+a[i];
25         if (check(mid)) l=mid; else r=mid;
26         for (int i=1;i<=n;i++) a[i]+=mid;
27     }
28     printf("%.5lf",l);
29 }