#include <bits/stdc++.h>
using namespace std;
int n, i, j, k, l, m;
double a[5050], s[5050], ma = -0x3f3f3f3f;
int main() {
  scanf("%d%d", &n, &k);
  for (i = 0; i < n; i++) {
    scanf("%lf", &a[i]);
    if (i == 0)
      s[i] = a[i];
    else
      s[i] = s[i - 1] + a[i];
  }
  for (i = 0; i + k - 1 < n; i++) {
    for (j = i + k - 1; j < n; j++) {
      if (i == 0)
        ma = max(ma, (s[j]) / (j - i + 1));
      else
        ma = max(ma, (s[j] - s[i - 1]) / (j - i + 1));
    }
  }
  printf("%.8lf", ma);
}
