#include <bits/stdc++.h>
using namespace std;
int a[5100], sum[5100];
int main() {
  int i, j, k;
  int n, m, t;
  scanf("%d%d", &n, &k);
  for (i = 1; i <= n; i++) scanf("%d", &a[i]);
  memset(sum, 0, sizeof(sum));
  for (i = 1; i <= n; i++) sum[i] = sum[i - 1] + a[i];
  double mx = 0.0, temp;
  for (i = 1; i <= (n - k + 1); i++) {
    for (j = k + i - 1; j <= n; j++) {
      temp = (sum[j] - sum[i - 1]) * 1.0;
      temp /= (j - i + 1);
      mx = max(mx, temp);
    }
  }
  cout << setprecision(15) << mx;
  return 0;
}
