#include <bits/stdc++.h>
using namespace std;
#define int long long
int n, lt;
int a[100010], sum[100010];

signed main() {
    cin >> n >> lt;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        a[i] *= 1000;
        sum[i] = sum[i - 1] + a[i];
    }
    double ans = 0;
    for (int i = 1; i <= n - lt + 1; i++) {
        int l = lt, r = n - i + 1;
        while (l <= r) {
            int mid = l + r >> 1;
            if ((sum[i + mid - 1] - sum[i - 1]) / mid > ans) ans = (sum[i + mid - 1] - sum[i - 1]) / mid, l = mid + 1;
            else r = mid -1;
        }
    }
    cout << ans;
    return 0;
}

70pts