include<bits/stdc++.h>

define ll long long

using namespace std;

int n ,k;
double a[300005];
double sum[300005];
bool check(double mid){
for(int i=1; i<=n; i++){
double value = a[i] - mid;
sum[i]= sum[i-1]+value;
}
double minVale= 1000001;
for(int i=k; i<=n; i++){
if(minVale > sum[i-k]){
minVale=sum[i-k];
}else if (minVale <= sum[i-k]){
return true;
}
}
return false;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cin>>n>>k;
double lo =0.0, h=1000000.000000;
for(int i=1; i<=n; i++){
double t; cin>>t;
a[i]=t;

}

for(int step=1; step<=500; step++){
    double mid= (lo+h)/2.0;
    if(check(mid)){
        lo=mid;
    }else{
        h=mid;
    }
}
// cout<<"hello";
cout << std::fixed << std::setprecision(6) << lo;

}