#include <bits/stdc++.h>
const int N = 1e5 + 5;
using namespace std;
long long int power(long long int x, long long int y) {
  long long int res = 1;
  while (y > 0) {
    if (y & 1) {
      res = (res * x) % 1000000007;
    }
    x = (x * x) % 1000000007;
    y = y >> 1;
  }
  return res;
}
std::vector<int> divi[60004];
void divisor(int n) {
  for (int i = 1; i <= n; i++) {
    for (int j = i; j <= n; j += i) {
      divi[j].push_back(i);
    }
  }
}
double a[100005];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, k;
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    a[i] = (double)x;
  }
  double val = 0.0;
  double ans = 0.0;
  for (int len = k; len <= n; len++) {
    val = 0.0;
    for (int i = 0; i < len; i++) {
      val = val + a[i];
    }
    double x = (double)len;
    double t = val / x;
    ans = max(ans, t);
    for (int i = len; i < n; i++) {
      val = val + a[i];
      val = val - a[i - len];
      t = val / x;
      ans = max(ans, t);
    }
  }
  printf("%.10f\n", ans);
  return 0;
}
