#include <bits/stdc++.h>
using namespace std;
const int maxn = 5010;
int n, k;
double num[maxn];
int main() {
  while (scanf("%d%d", &n, &k) != EOF) {
    int a;
    memset(num, 0, sizeof(num));
    for (int i = 1; i <= n; i++) {
      scanf("%d", &a);
      num[i] = num[i - 1] + a;
    }
    double ans = 0;
    for (int i = 1; i <= n; i++)
      for (int j = i + k - 1; j <= n; j++)
        ans = max(ans, (num[j] - num[i - 1]) / (j - i + 1));
    printf("%.6lf\n", ans);
  }
  return 0;
}
