#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int MAX_N = 200000 + 5;

int N, M, a[MAX_N], g[MAX_N], ql[MAX_N], qr[MAX_N];
ll sum[MAX_N];
double f[MAX_N];

inline double w(int i, int j) {
    return sqrt((sum[j] - sum[i]) * (j - i)) + f[i];
}

void dp(double pen) {
    static int q[MAX_N];
    int hd = 0, tl = 0;
    ql[0] = 1; qr[0] = N;
    for (int i = 1; i <= N; i ++) {
        while (hd <= tl && qr[q[hd]] < i) hd ++;
        f[i] = w(q[hd], i) + pen;
        g[i] = g[q[hd]] + 1;
        while (hd <= tl && w(i, ql[q[tl]]) <= w(q[hd], ql[q[tl]])) tl --;
        if (tl < hd) {
            q[++ tl] = i;
            ql[i] = i + 1;
            qr[i] = N;
        }else if (w(q[tl], qr[q[tl]]) < w(i, qr[q[tl]])) {
            if (qr[q[tl]] < N) {
                ql[i] = qr[q[tl]] + 1;
                qr[i] = N;
                q[++ tl] = i;
            }
        }else {
            int l = ql[q[tl]], r = qr[q[tl]];
            while (l < r) {
                int mid = l + r >> 1;
                if (w(i, mid) < w(q[tl], mid)) r = mid;
                else l = mid + 1;
            }
            qr[q[tl]] = l;
            ql[i] = l + 1;
            qr[i] = N;
            q[++ tl] = i;
        }
    }
}

int main() {
    scanf("%d%d", &N, &M);
    for (int i = 1; i <= N ; i ++) {
        scanf("%d", a + i);
    }
    sort(a + 1, a + N + 1);
    for (int i = 1; i <= N; i ++) {
        sum[i] = sum[i - 1] + a[i];
    }
    double l = 0, r = 1e18;
    while (r - l > 1e-7) {
        double mid = (l + r) / 2;
        dp(mid);
        if (g[N] <= M) r = mid;
        else l = mid;
    }
    dp(r);
    printf("%.15lf\n", f[N] - g[N] * r);
    return 0;
}