#include <bits/stdc++.h>
using namespace std;
int gi() {
  int a;
  scanf("%d", &a);
  return a;
}
long long gli() {
  long long a;
  scanf("%I64d", &a);
  return a;
}
int s[5001];
double divv(double a, double b) { return a / b; }
int main() {
  int n = gi();
  int k = gi();
  s[0] = 0;
  for (int i = 0; i < n; i++) s[i + 1] = s[i] + gi();
  double r = 0;
  for (int i = 0; i < n; i++)
    for (int j = i + k; j <= n; j++) {
      double a = divv(s[j] - s[i], j - i);
      r = (a > r ? a : r);
    }
  printf("%.9lf\n", r);
  return 0;
}
