#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n, k;
  cin >> n >> k;
  vector<long double> v(n + 1, 0.0);
  for (long long i = 1; i <= n; i++) {
    cin >> v[i];
  }
  vector<long double> v2(n + 1, 0);
  v2[1] = v[1];
  for (long long i = 2; i <= n; i++) {
    v2[i] = v2[i - 1] + v[i];
  }
  long double ans = 0.0;
  for (long long i = 1; i <= n; i++) {
    for (long long j = i; j <= n; j++) {
      if ((j - i + 1) >= k) {
        long double x1 = (v2[j] - v2[i - 1]) * 1.0;
        long double x2 = (j - i + 1) * 1.0;
        long double ans1 = x1 / x2;
        ans = max(ans, ans1);
      }
    }
  }
  cout << fixed << setprecision(20) << ans << endl;
  return 0;
}
