#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const int INF = 1e9 + 7;
const long long LINF = 2e18 + 7;
const int MXN = 20;
void io() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
}
int v[5005];
int main() {
  int N, K;
  cin >> N >> K;
  for (int i = 1; i <= N; ++i) {
    cin >> v[i];
    v[i] += v[i - 1];
  }
  double ans = -1e100;
  for (int i = 1; i <= N; ++i) {
    for (int j = i + K - 1; j <= N; ++j) {
      double cur = (double)(v[j] - v[i - 1]) / (j - i + 1);
      ans = max(ans, cur);
    }
  }
  cout << fixed;
  cout.precision(10);
  cout << ans;
}
