#include <bits/stdc++.h>
using namespace std;
vector<int> arr;
int n, k;
long long sum[5500];
double mx = -1e9;
int main() {
  cin >> n >> k;
  for (int x, i = 1; i <= n; i++) {
    cin >> x;
    arr.push_back(x);
    sum[i] = sum[i - 1] + x;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i + k - 1; j <= n; j++) {
      mx = max(mx, (sum[j] - sum[i - 1]) / (double(j - i + 1)));
    }
  }
  printf("%0.15lf", mx);
}
