#include <bits/stdc++.h>
using namespace std;
#define int long long

int n, k;
int x[205], y[205];

double dist(double x1, double y1, double x2, double y2){
         double dx = x1 - x2;
         double dy = y1 - y2;
         return sqrt(dx * dx + dy * dy);
}
pair<double, double> F2(double X, double Y){
         double sum = 0;
         int I[n];
         iota(I, I + n, 0);
         sort(I, I + n, [&](int i, int j){
                  return dist(X, Y, x[i], y[i]) > dist(X, Y, x[j], y[j]);
         });

         for(int i = 0; i < k; i++){
                  sum += dist(X, Y, x[I[i]], y[I[i]]);
         }
         return {-sum, Y};
}
pair<double, double> f(double x){
         double l = -1000, r= 1000;
         for(int i = 0; i < 100; i++){
                  double m1 = l + (r - l) / 3;
                  double m2 = r - (r - l) / 3;
                  auto f1 = F2(x, m1);
                  auto f2 = F2(x, m2);
                  if (f1 < f2)
                           l = m1;
                  else
                           r = m2;
         }
         return {F2(x, l).first, x};
}
void solve() {
         cin>>n>>k;
         for(int i = 0; i < n; i++){
                  cin>>x[i]>>y[i];
         }

         double l = -1000, r= 1000;
         for(int i = 0; i < 100; i++){
                  double m1 = l + (r - l) / 3;
                  double m2 = r - (r - l) / 3;
                  auto f1 = f(m1);      //evaluates the function at m1
                  auto f2 = f(m2);      //evaluates the function at m2
                  if (f1 < f2)
                           l = m1;
                  else
                           r = m2;
         }
         cout<<fixed<<setprecision(10);
         cout<<-f(l).first<<"\n";
}

int32_t main() {
         cin.tie(0);
         cout.sync_with_stdio(0);

         solve();
}