#include <bits/stdc++.h>
using namespace std;
const long long N = 5001;
long long A[N];
long long ac[N];
int main() {
  long long n, k;
  cin >> n >> k;
  for (long long i = 0; i < n; i++) {
    cin >> A[i];
  }
  ac[0] = A[0];
  for (long long i = 1; i < n; i++) {
    ac[i] = ac[i - 1] + A[i];
  }
  long double mx = 0.0;
  for (long long i = k; i <= n; i++) {
    for (long long j = i - 1; j < n; j++) {
      if (j - i < 0) {
        long double aux = (ac[j] * 1.0) / (i * 1.0);
        mx = max(mx, aux);
      } else {
        long double aux = (ac[j] * 1.0 - ac[j - i] * 1.0) / (i * 1.0);
        mx = max(mx, aux);
      }
    }
  }
  printf("%.15Lf\n", mx);
  return 0;
}
