#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
typedef long long ll;
const int SIZEN=100010;
int N,K;
ll S[SIZEN]={0};
ll segsum(int i,int j){
	return S[j]-S[i-1];
}
double aver(int i,int j){
	return (segsum(i,j)+0.0)/(j-i+1+0.0);
}
void work(void){
	double ans=0;
	int now=1;
	for(int i=K;i<=N;i++){
		double a1=aver(now,i),a2=aver(i-K+1,i);
		if(a2>a1) now=i-K+1,ans=max(ans,a2);
		else ans=max(ans,a1);
	}
	ll temp=ans*1000;
	printf("%lld\n",temp);
}
void read(void){
	scanf("%d%d",&N,&K);
	for(int i=1;i<=N;i++) scanf("%d",&S[i]),S[i]+=S[i-1];
}
int main(){
	freopen("helpz.in","r",stdin);
	freopen("helpz.out","w",stdout);
	read();
	work();
	return 0;
}