#include <bits/stdc++.h>
using namespace std;
int main() {
  cout.setf(ios::fixed);
  cout.precision(15);
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  int n, k;
  cin >> n >> k;
  vector<long long> V(n);
  vector<long long> A(n, 0);
  for (int i = 0; i < n; i++) {
    cin >> V[i];
    if (i != 0)
      A[i] = A[i - 1] + V[i];
    else
      A[i] = V[i];
  }
  long double ma = 0;
  for (int i = 0; i < n; i++) {
    for (int j = i + k - 1; j < n; j++) {
      int s = A[j];
      if (i != 0) s -= A[i - 1];
      int d = j - i + 1;
      long double a = 1.0 * s / d;
      if (a > ma) ma = a;
    }
  }
  cout << ma << endl;
}
