#include <bits/stdc++.h>
using namespace std;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << ": " << arg1 << " |";
  __f(comma + 1, args...);
}
const int LOGN = 51;
const long long INF = (1e15) + 10;
const long long MOD = 998244353;
const double PI = acos(-1.0);
const double EPS = 1e-12;
const long long maxn = 1e2 + 10;
const long long maxm = (long long)1e6;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n, k;
  while (cin >> n >> k) {
    vector<int> a(n + 1);
    for (int i = (0); i < ((n)); ++i) cin >> a[i + 1];
    vector<int> s(n + 1);
    for (int i = (0); i < ((n)); ++i) s[i + 1] = s[i] + a[i + 1];
    double ans = 0;
    for (int i = (1); i <= (n); ++i) {
      for (int j = (i + k - 1); j <= (n); ++j) {
        double avg = (double)(s[j] - s[i - 1]) / (j - i + 1);
        (ans) = max((ans), (avg));
      }
    }
    printf("%.6f\n", ans);
  }
  return 0;
}
