qwq，写的凸包，三个hack数据一个没过，其他的都过了。

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=2e5+7;
struct Node
{
	int x,y;
	bool operator != (Node a)
	{
		if(a.x==x&&a.y==y) return 0;
		return 1;
	}
	bool operator == (Node a)
	{
		if(a.x==x&&a.y==y) return 1;
		return 0;
	}
}a[N],st[N];
int top,k;
inline int Dis(Node A,Node B)
{
	int ans=(B.x-A.x)*(B.x-A.x)+(B.y-A.y)*(B.y-A.y);
	return (ans);
}
inline int check(Node A1,Node A2,Node B1,Node B2)
{
	return (A2.x-A1.x)*(B2.y-B1.y)-(B2.x-B1.x)*(A2.y-A1.y);
}
inline int check2(Node A1,Node A2,Node B1,Node B2)
{
	int ans1=check(A1,A2,B1,B2);
	if(ans1==0)
		return Dis(A1,A2)-Dis(B1,B2);
	return ans1;
}
int n;
long double ans;
inline bool cmp(Node A,Node B)
{
	int pd=check(a[1],A,a[1],B);
	if(pd>0)
		return 1;
	if(pd==0&&Dis(a[0],A)<Dis(a[0],B))
		return 1;
	return 0;
}
inline long double S(Node A,Node B,Node C)
{
	long double AA=(long double)sqrt(Dis(A,B));
	long double BB=(long double)sqrt(Dis(A,C));
	long double CC=(long double)sqrt(Dis(B,C));
	long double PP=(long double)(AA+BB+CC)/2.0;
	return (long double)sqrt((long double)PP*(long double)(PP-AA)*(long double)(PP-BB)*(long double)(PP-CC));
}
inline void del(int x)
{
	for(int i=1;i<=n;i++)
	{
		if(a[i]==st[x])
		{
			for(int j=i+1;j<=n;j++)
			{
				a[j-1]=a[j];
			}
			a[n]={0,0};
			n--;
			return;
		}
	}
}
priority_queue<int,vector<int>,greater<int> > q;
signed main()
{
	scanf("%lld %lld",&n,&k);
	for(int i=1;i<=n;i++)
		scanf("%lld %lld",&a[i].x,&a[i].y);
	for(int cs=1;cs<=k;cs++)
	{
		top=0;
		memset(st,0,sizeof(st));
		for(int i=1;i<=n;i++)
		{
			if(i!=1&&(a[i].y<a[1].y||(a[i].y==a[1].y&&a[i].x<a[1].x)))
			{
				Node s=a[1];
				a[1]=a[i];
				a[i]=s;
			}
		}
		sort(a+2,a+1+n,cmp);
		st[++top]=a[1];
		for(int i=2;i<=n;i++)
		{
			while(top>1&&check2(st[top-1],st[top],st[top],a[i])<=0)
				top--;
			st[++top]=a[i];
		}
		st[top+1]=a[1];
		int j=2;
		int ans=0;
		int id1=-1,id2=-1;
		if(top==2)
		{
			id1=1;
			id2=2;
			ans=Dis(st[1],st[2]);
		}
		for(int i=1;i<=top;i++)
		{
			ans=max(ans,Dis(st[i],st[i+1]));
			while((long double)S(st[i],st[i+1],st[j])<(long double)S(st[i],st[i+1],st[j+1]))
			{
				j++;
				if(j>top)
				j=1;
			}
			int v1=Dis(st[i],st[j]),v2=Dis(st[i+1],st[j]);
			if(v1>ans)
			{
				ans=v1,id1=i,id2=j;
			}
			if(v2>ans)
			{
				ans=v2,id1=i+1,id2=j;
			}
			ans=max(ans,max(v1,v2));
		}
		q.push(ans);
		if(q.size()>k) q.pop();
		for(int i=1;i<=n;i++)
		{
			if(a[i]!=st[id1]&&a[i]!=st[id2])
			{
				q.push(Dis(a[i],st[id1]));
			}
			if(q.size()>k) q.pop();
		}
		for(int i=1;i<=n;i++)
		{
			if(a[i]!=st[id1]&&a[i]!=st[id2])
				q.push(Dis(a[i],st[id2]));
			if(q.size()>k) q.pop();
		}
		del(id1);
		del(id2);
	}
	printf("%lld\n",q.top());
}