#include <bits/stdc++.h>
using namespace std;
long long gcd(long long a, long long b) {
  if (!a) return b;
  return gcd(b % a, a);
}
long long power(long long x, long long n) {
  if (x == 0) return 0;
  if (n == 0) return 1;
  if (n == 1) return x;
  long long res = power(x, n / 2);
  res = (res * res) % 1000000007;
  if (n % 2) return (res * x) % 1000000007;
  return res;
}
long long nCr(long long n, long long r) {
  if (r == 0) return 1;
  vector<long long> f(n + 1);
  f[0] = 1;
  for (long long i = 1; i <= n; i++) f[i] = (f[i - 1] * i) % 1000000007;
  return ((f[n] * power(f[r], 1000000007 - 2)) % 1000000007 *
          power(f[n - r], 1000000007 - 2)) %
         1000000007;
}
const long long MAX = 1000001;
long long factor[MAX] = {0};
void gen_Prime_Fac() {
  factor[1] = 1;
  for (long long i = 2; i < MAX; i++) factor[i] = i;
  for (long long i = 4; i < MAX; i += 2) factor[i] = 2;
  for (long long i = 3; i * i < MAX; i++) {
    if (factor[i] == i) {
      for (long long j = i * i; j < MAX; j += i) {
        if (factor[j] == j) factor[j] = i;
      }
    }
  }
}
long long no_of_fac(long long n) {
  if (n == 1) return 1;
  long long ans = 1;
  long long dup = factor[n];
  long long c = 1;
  long long j = n / factor[n];
  while (j != 1) {
    if (factor[j] == dup)
      c += 1;
    else {
      dup = factor[j];
      ans = ans * (c + 1);
      c = 1;
    }
    j /= factor[j];
  }
  ans *= (c + 1);
  return ans;
}
bool is_pow_2(long long n) {
  long long i = 1;
  while (i < n) {
    i *= 2;
  }
  return i == n;
}
int32_t main() {
  long long n, k;
  cin >> n >> k;
  vector<long double> pref(n);
  long double sum = 0;
  for (long long i = 0; i < n; i++) {
    long double x;
    cin >> x;
    sum += x;
    pref[i] = sum;
  }
  long double ans = 0;
  for (long long i = k; i <= n; i++) {
    long double sum = pref[i - 1];
    for (long long j = i; j < n; j++) {
      sum = max(sum, (pref[j] - pref[j - i]));
    }
    ans = max(ans, sum / i);
  }
  cout << fixed << setprecision(10) << ans;
}
