Description：

Solution：

Code：

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<cstring>

using namespace std;

int n,k;

#define MAXN 1010

double x[MAXN],y[MAXN];

struct edge

{

    int u,v;

    double d;

}e[MAXN * MAXN];

int edgenum = 0;

inline void add(int a,int b,double c){++edgenum;e[edgenum].u = a;e[edgenum].v = b;e[edgenum].d = c;return;}

inline double dis(int a,int b){return sqrt((x[a] - x[b]) * (x[a] - x[b]) + (y[a] - y[b]) * (y[a] - y[b]));}

int f[MAXN];

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

bool cmp(edge a,edge b){return a.d < b.d;}

int main()

{

    scanf("%d%d",&n,&k);

    for(int i = 1;i <= n;++i)

    {

        scanf("%lf%lf",&x[i],&y[i]);

    }

    for(int i = 1;i <= n;++i)

    {

        for(int j = i  + 1;j <= n;++j)

        {

            add(i,j,dis(i,j));

        }

    }

    for(int i = 1;i <= n;++i)

    {

        f[i] = i;

    }

    int siz = n;

    sort(e + 1,e + 1 + edgenum,cmp);

    int i;

    for(i = 1;i <= edgenum && siz != k;++i)

    {

        if(find(e[i].u) == find(e[i].v))continue;

        f[find(e[i].u)] = find(e[i].v);

        --siz;

    }

    while(find(e[i].u) == find(e[i].v))++i;

    printf("%.2f\n",e[i].d);

    return 0;

}