#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;
struct bian
{
	int begine;
	int to;
	long long pre;
}line[4000001];
int m,n,q=0,k=1;
int fat[4000001];
int x[2005],y[2001];
//bool a[5003]={0};
long long tot=0;
int father(int x)
{
	if(fat[x]!=x) fat[x]=father(fat[x]);
	return fat[x];	
}
void unionn(int x,int y)
{
	int fa=father(x);
	int fb=father(y);
	if(fa!=fb) fat[fa]=fb;
}
long long cmp(bian a,bian b)
{
	if(a.pre<b.pre) return 1;
	else return 0;
}
int change(int x,int y);
int main()
{
	int log=0,c;
	//freopen("in.txt","r",stdin);
	//freopen("o.txt","w",stdout);
	cin>>n>>c;
	for(int i=1;i<=n;i++){
		cin>>x[i]>>y[i];
		for(int j=1;j<i;j++){
			int dis=(x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]);
			if(dis>=c){
				//sqrt(dis);
				q++;
				line[q].begine=i;
				line[q].to=j;
				line[q].pre=dis;
			}
		}
	}
	if(q<n)cout<<"-1";
	else{
		sort(line+1,line+q+1,cmp);
	for(int i=1;i<=n;i++) fat[i]=i;

		for(int i=1;i<=q;i++){
		if(father(line[i].begine)!=father(line[i].to)){
			unionn(line[i].begine,line[i].to);
			tot+=line[i].pre;
			k++;
		}
		if(k==n) break;
	}
	if(k<n) cout<<"-1";
		else cout<<tot;
	}
	
	return 0;
}