#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k, i, j, l;
  cin >> n >> k;
  double a[n + 1], b, s = 0, r = -1;
  a[0] = 0;
  for (i = 1; i <= n; i++) {
    cin >> b;
    s += b;
    a[i] = s;
  }
  for (i = k; i <= n; i++) {
    l = 1;
    for (j = i; j <= n; j++) {
      r = max(r, (a[j] - a[l - 1]) / i);
      l++;
    }
  }
  printf("%.10f", r);
  return 0;
}
