CODE

#include <bits/stdc++.h>
using namespace std;
const int N = 500;
const int M = (N * (N - 1)) >> 1;
int s,p,m,cnt;
double ans;
int f[N + 10], x[N + 10], y[N + 10];

int find (int x) {
	return f[x] == x ? x : f[x] = find(f[x]);
}

struct edge {
	double w;
	int u, v;
	friend bool operator<(edge x, edge y)  {
		return x.w < y.w;
	}
}e[M + 10];

void kruskal (){
	sort(e + 1, e + m +1);
	for (int i = 1; i <= m; i++) {
		int fu = find(e[i].u),fv = find (e[i].v);
		if (fu == fv)
			continue;
		f[fu] = fv;
		ans = e[i].w;
		cnt++;
		if (cnt == p - s)
			return;
	}
}
int main () {
	cin >> s >> p;
	for (int i = 1; i <= p; i++)
		cin >> x[i] >> y[i],f[i] = i;
	for (int i = 1; i <= p; i++)
	 	for (int j = i +1; j <= p; j++)
	 		e[++m].u = i, e[m].v = j, e[m].w = sqrt((x[i] - x[j]) * (x[i] - x[j]) + (y[i] * y[j]) * (y[i] * y[j]));
	kruskal();
	cout << ans;
}