LAH28_AVERAGE

/*#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,avx2,fma")*/
// only when really needed

/* GNU G++17 7.3.0: No long long for faster code
   GNU G++17 9.2.0 (64 bit, msys 2): Long long only for faster code */

#include <bits/stdc++.h>

#define for1(i,a,b) for (int i = a; i <= b; i++)
#define for2(i,a,b) for (int i = a; i >= b; i--)
#define int long long

#define sz(a) (int)a.size()
#define pii pair<int,int>

/*
__builtin_popcountll(x) : Number of 1-bit
__builtin_ctzll(x) : Number of trailing 0
*/

#define PI 3.1415926535897932384626433832795
#define INF 1000000000000000000
#define MOD 1000000007
#define MOD2 1000000009
#define EPS 1e-6

using namespace std;

double a[100005];
int n, k;

signed main() {

    ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);

    freopen("average.inp", "r", stdin);
    freopen("average.out", "w", stdout);

    cin >> n >> k;
    for1(i,1,n) {
        int x;
        cin >> x;
        a[i] = double(x);
    }

    double l = 0, r = 1e9;
    for1(i,1,100) {

        double m = (l + r)/2, sum = 0, sum2 = 0, mn = 0;
        bool flag = false;

        for1(i,1,k) sum += a[i] - m;
        for1(i,k+1,n) {
            sum += a[i] - m;
            sum2 += a[i - k] - m;
            if (sum2 < mn) mn = sum2;
            if (sum - mn + EPS > 0) flag = true;
        }

        if (flag) l = m;
        else r = m;

    }

    cout << fixed << setprecision(4) << l;

}