#include <bits/stdc++.h>
using namespace std;
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
const int N = 2e5 + 10, OO = 0x3f3f3f3f;
int a[N];
void _run() {
  int n, k;
  cin >> n >> k;
  for (int i = 0; i < n; ++i) cin >> a[i];
  double ans = 0;
  for (int i = 0; i <= n - k; ++i) {
    int sum = 0, cnt = 0;
    for (int j = i; j < n; ++j) {
      sum += a[j], cnt++;
      if (cnt >= k) {
        double avg = (sum * 1.0) / (j - i + 1);
        ans = max(ans, avg);
      }
    }
  }
  cout << fixed << setprecision(9) << ans << "\n";
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int tc = 1;
  while (tc--) {
    _run();
  }
  return 0;
}
