#include <bits/stdc++.h>
using namespace std;
bool is_prime(int n) {
  for (int i = 2; i * i <= n; ++i) {
    if (n % i == 0) {
      return false;
    }
  }
  return true;
}
inline long long getPow(long long a, long long b) {
  long long res = 1, tp = a;
  while (b) {
    if (b & 1ll) {
      res *= tp;
      res %= 1000000007;
    }
    tp *= tp;
    tp %= 1000000007;
    b >>= 1ll;
  }
  return res;
}
inline long long nxt() {
  long long x;
  scanf("%lld", &x);
  return x;
}
void ok() {
  puts("YES");
  exit(0);
}
void no() {
  puts("NO");
  exit(0);
}
long long xx[] = {-1, 1, 0, 0};
long long yy[] = {0, 0, -1, 1};
int main() {
  long long n = nxt(), k = nxt();
  double ans = 0;
  unsigned long long sum = 0;
  vector<int> mas(n);
  for (int i = 0; i < n; i++) mas[i] = nxt();
  for (k; k <= n; k++) {
    sum = 0;
    for (int i = 0; i < k; i++) sum += mas[i];
    if (ans < (double)sum / k) ans = (double)sum / k;
    for (int i = 1; i < n - k + 1; i++) {
      sum += mas[i + k - 1];
      sum -= mas[i - 1];
      if (ans < (double)sum / k) ans = (double)sum / k;
    }
  }
  cout << setprecision(18) << ans;
  return 0;
}
