#include <bits/stdc++.h>
const static long long INF = 0x3f3f3f3f3f3f3f3f;
static inline void setio(void);
long long n, k;
int a[5001];
int aa[5001][5001];
int main(void) {
  setio();
  std::cin >> n >> k;
  for (long long i = 0; i < n; ++i) std::cin >> a[i];
  for (long long i = 0; i < n; ++i) {
    long long sum = 0;
    for (long long j = i; j < n; ++j) {
      sum += a[j];
      aa[i][j] = sum;
    }
  }
  double best = 0;
  for (long long i = 0; i < n; ++i) {
    for (long long j = i + k - 1; j < n; ++j) {
      double tmp = aa[i][j];
      tmp /= (j - i + 1);
      best = std::max(best, tmp);
    }
  }
  std::cout << best << "\n";
  return 0;
}
static inline void setio(void) {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::cout.precision(10);
  std::cout << std::fixed;
}
