```cpp
#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<queue>
#include<string>
#include<bitset>
#include<cctype>
#include<cstdlib>
#include<functional>
#include<istream>
#include<sstream>
#include<streambuf>
#define ll long long
using namespace std;
const int N=200000,inf=0x3f3f3f;
struct edge
{
double head,to,w;
bool operator < (const edge &x) const
{
return w<x.w;
}
}e[N];
int x[N],y[N],f[N],s,p,cnt=0,n=0;
double ans=0;
//bool cmp(edge a,edge b)
//{
// return a.w<b.w;
//}
double dis(int i,int j)
{
return sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
}
int find1(int x)
{
return f[x]==x?x:f[x]=find1(f[x]);
}
void Kruskal()
{
for(int i=1;i<=p;i++)
f[i]=i;
sort(e+1,e+1+n);
for(int i=1;i<=n;i++)
{
// printf("%d--%d--%.2lf\n",i,cnt,e[i].w);
double x=e[i].head,y=e[i].to,z=e[i].w;
int tx=find1(x),ty=find1(y);
if(tx!=ty)
{
f[tx]=ty;
ans=max(ans,z);
cnt++;
if(cnt>=p-s)
break;
}
}
}
int main()
{
scanf("%d%d",&s,&p);
for(int i=1;i<=p;i++)
{
scanf("%d%d",&x[i],&y[i]);
for(int j=1;j<i;j++)
{
n++;
e[n]={i,j,dis(i,j)};
}
}
Kruskal();
printf("%.2f",ans);
return 0;
}
by AlexSong @ 2023-08-27 17:19:16