/**
* Author: Praveen Ojha
* Created: 11 February 2019
* Time: 01:12:49
**/
#include <stdio.h>
using namespace std;
#define mod 1000000007
#define PI 3.141592653589793238510
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define __ ios_base::sync_with_stdio(false);cin.tie(NULL);
typedef long long ll;
typedef long double ld;
int main(){//__
ll n,k;
scanf("%lld %lld",&n,&k);
ll a[n+1];
a[0]=0;
for(ll i=1;i<=n;i++){
scanf("%lld",&a[i]);
}
ld maxi=0;
for(ll i=2;i<=n;i++){
a[i]+=a[i-1];
}
for(ll i=k;i<=n;i++){
//cout<<"k:"<<i<<"\n";
for(ll start=1;start+i-1<=n;start++){
ld sumi=a[start+i-1]-a[start-1];
//cout<<"\n";
sumi=(ld)sumi/(ld)i;
if(sumi>maxi)
maxi=sumi;
}
}
printf("%.10Lf\n",maxi);
return 0;
}
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