#include <bits/stdc++.h>
using namespace std;
int n, k, a[5050];
double ans = 0.0;
void f(int pos) {
  int t, sum = 0;
  for (int i = pos; i <= n; i++) {
    sum += a[i];
    t++;
    if (t >= k) {
      double tp = (double)sum / (double)t;
      ans = max(ans, tp);
    }
  }
}
int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  for (int i = 1; i <= n; i++) {
    f(i);
  }
  printf("%.9lf", ans);
  return 0;
}
