#include <bits/stdc++.h>
using namespace std;
long long dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
long long ddx[8] = {1, 1, 0, -1, -1, -1, 0, 1},
          ddy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
long long gcd(long long a, long long b) {
  if (!a) return b;
  return gcd(b % a, a);
}
long long lcm(long long a, long long b) { return (a * b) / gcd(a, b); }
long double fun(vector<long long> arr, long long k) {
  long double div = k;
  long double temp = 0;
  long double ma = 0;
  for (long long i = 0; i < k; i++) {
    temp += arr[i];
  }
  ma = temp / div;
  for (long long i = k; i < arr.size(); i++) {
    temp += arr[i];
    temp -= arr[i - k];
    ma = max(ma, temp / div);
  }
  return ma;
}
void test_case() {
  long long n;
  cin >> n;
  long long k;
  cin >> k;
  vector<long long> arr(n);
  for (long long i = 0; i < (long long)(n); i++) {
    cin >> arr[i];
  }
  long double ans = 0;
  for (long long i = k; i <= n; i++) {
    long double val = fun(arr, i);
    ans = max(ans, val);
  }
  cout << ans << "\n";
}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(20);
  long long t = 1;
  while (t--) {
    test_case();
  }
}
