#include <bits/stdc++.h>
using namespace std;
using llf = long double;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    int n, k; cin >> n >> k;
    vector<pair<int, int>> a(n);
    for (auto &[x, y] : a) cin >> x >> y;

    auto f = [&](llf x, llf y){
        vector<llf> ans(n);
        for (int i = 0; i < n; ++i) {
            ans[i] = hypot(x - a[i].first, y - a[i].second);
        }
        nth_element(ans.begin(), ans.begin() + k, ans.end(), greater<>());
        llf s = 0;
        for (int i = 0; i < k; ++i)
            s += ans[i];
        // cout << x << ", " << y << ": " << s << '\n';
        return s;
    };

    //mt19937 rnd_engine(7122);
    //uniform_real_distribution<llf> rnd(0, 1);
    //uniform_real_distribution<llf> C(-1000, 1000);
    //uniform_real_distribution<llf> d(-10, 10);
    //static constexpr llf dT = 0.1, EPS = 1e-2;
    auto solve_y = [&](llf x) {
        llf L = -1000, R = 1000;
        for (int iter = 0; iter < 200; ++iter) {
            llf M1 = L + (R - L) / 3;
            llf M2 = R - (R - L) / 3;
            llf v1 = f(x, M1);
            llf v2 = f(x, M2);
            if (v1 < v2) R = M2;
            else L = M1;
        }
        return f(x, L);
        //llf y = C(rnd_engine);
        //llf S_cur = f(x, y);
        //llf S_best = S_cur;
        //for (llf T = 100; T > EPS; T -= dT) {
        //    llf y_prime = y + d(rnd_engine) * T;
        //    const llf S_prime = f(x, y_prime);
        //    const llf delta_c = S_prime - S_cur;
        //    llf prob = min<llf>(1, exp(-delta_c / T));
        //    if (rnd(rnd_engine) <= prob or S_prime < S_cur)
        //        S_cur = S_prime, y = y_prime;
        //    if (S_prime < S_best)
        //        S_best = S_prime;
        //}
        //return S_best;
    };
    auto solve = [&]{
        llf L = -1000, R = 1000;
        for (int iter = 0; iter < 200; ++iter) {
            llf M1 = L + (R - L) / 3;
            llf M2 = R - (R - L) / 3;
            llf v1 = solve_y(M1);
            llf v2 = solve_y(M2);
            if (v1 < v2) R = M2;
            else L = M1;
        }
        return solve_y(L);
        //llf x = C(rnd_engine);
        //llf S_cur = solve_y(x);
        //llf S_best = S_cur;
        //for (llf T = 100; T > EPS; T -= dT) {
        //    llf x_prime = x + d(rnd_engine) * T;
        //    const llf S_prime = solve_y(x);
        //    const llf delta_c = S_prime - S_cur;
        //    llf prob = min<llf>(1, exp(-delta_c / T));
        //    if (rnd(rnd_engine) <= prob or S_prime < S_cur)
        //        S_cur = S_prime, x = x_prime;
        //    if (S_prime < S_best)
        //        S_best = S_prime;
        //}
        //return S_best;
    };

    cout << fixed << setprecision(10) << solve() << '\n';
    return 0;
}