#include<bits/stdc++.h>

 #define F(i,a,b) for(int i=a;i<=b;++i)

 using namespace std;

 int tot;

 const int BUF=;

 char Buf[BUF],*buf=Buf;

 inline void read(int&a){for(a=;*buf<;buf++);while(*buf>)a=a*+*buf++-;}

 const int N=1e5+;

 int sum[N],Q[N],n,k;

 inline int useless(int a,int b,int c)

 {

     return 1ll*(sum[c]-sum[b])*(b-a)<=1ll*(sum[b]-sum[a])*(c-b);

 }

 int main()

 {

     tot=fread(Buf,,BUF,stdin);

     while()

     {

         if(buf-Buf+>=tot)break;

         read(n),read(k);

         F(i,,n)read(sum[i]),sum[i]+=sum[i-];

         int head=,tail=;

         double ans=;

         F(i,k,n)

         {

             while(head<tail&&useless(Q[tail-],Q[tail],i-k))tail--;

             Q[++tail]=i-k;

             while(head<tail&&useless(Q[head+],Q[head],i))head++;

             ans=max(ans,(sum[i]-sum[Q[head]])*1.0/(i-Q[head]));

         }

         printf("%.2f\n",ans);

     }

     return ;

 }