#include <bits/stdc++.h>
using namespace std;
void fileio() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  if (fopen("input.txt", "r")) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  }
}
const long double eps = 1e-7;
long long n, k, a[5005], pf[5005] = {0};
int main() {
  fileio();
  cin >> n >> k;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= n; i++) pf[i] = a[i] + pf[i - 1];
  double res = 0.0;
  for (int i = 1; i <= n; i++)
    for (int j = i + k - 1; j <= n; j++) {
      res = max(res, ((pf[j] - pf[i - 1]) * 1.0) / ((j - i + 1) * 1.0));
    }
  cout << fixed << setprecision(11) << res;
  return 0;
}
