#include <bits/stdc++.h>
using namespace std;
int main() {
  std::cout << std::fixed;
  std::cout.precision(6);
  int n, k;
  cin >> n >> k;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  float ans = 0;
  int pre[n];
  pre[0] = a[0];
  for (int i = 1; i < n; i++) pre[i] = pre[i - 1] + a[i];
  for (int start = 0; start < n; start++) {
    for (int end = start; end < n; end++) {
      if (end - start + 1 >= k) {
        int sum;
        if (!start)
          sum = pre[end];
        else
          sum = pre[end] - pre[start - 1];
        ans = max(ans, (float)sum / (end - start + 1));
      }
    }
  }
  cout << ans << "\n";
}
