#include <stdio.h>
#include <math.h>
#include <algorithm>
#include <utility>
#include <vector>
#include <queue>
using namespace std;
#define MN 600010
#define MM 3000010
int X[1010],Y[1010];double di[1010][1010];
double dis(int a,int b)
{
    return sqrt(1ll*a*a+1ll*b*b);
}
struct lin
{
    int x,y,i;
    void sw(){int t=x;x=y;y=t;}
}sz[1010];
bool operator<(const lin&a,const lin&b)
{
    return a.x<b.x;
} 
int cal(int n)
{
    if(n==1)return 1;
    int a=n/2,b=n-a;
    return 2*(cal(a)+cal(b))+a*b+a+b;
}
int fr[MN],ne[MM],v[MM],bs=0,N;double w[MM];
void addb(int a,int b,double c)
{
    //printf("(%d %d %.2lf)\n",a,b,c);
    v[bs]=b;
    w[bs]=c;
    ne[bs]=fr[a];
    fr[a]=bs++;
}
int wz[MN];vector<pair<int,int> > v3,v4;
void dfs(int l,int r,vector<pair<int,int> >&v1,vector<pair<int,int> >&v2,vector<int>&nd)
{
    sort(sz+l,sz+r+1);
    if(l==r)
    {
        int i=sz[l].i;fr[++N]=-1;
        v1.push_back(make_pair(i,N));
        v2.push_back(make_pair(i,N));
        nd.push_back(N);return;
    }
    if(l+1==r)
    {
        int i=sz[l].i,j=sz[l+1].i;
        fr[++N]=-1;fr[++N]=-1;
        v1.push_back(make_pair(i,N-1));
        v2.push_back(make_pair(j,N));
        nd.push_back(N);
        nd.push_back(N-1);
        addb(N-1,N,di[i][j]);
        return;
    }
    int m=(l+r+1)>>1;
    for(int i=l;i<=r;i++)sz[i].sw();
    vector<pair<int,int> > a,b,c,d;
    vector<int> nl,nr;
    dfs(l,m-1,a,b,nl);dfs(m,r,c,d,nr);
    int s=nl.size();
    for(int i=1;i<=s;i++)fr[N+i]=-1,wz[nl[i-1]]=i;
    for(int i=1;i<=s;i++)
    {
        int u=nl[i-1];
        for(int j=fr[u];j!=-1;j=ne[j])
            addb(N+wz[v[j]],N+i,w[j]);
    }
    for(auto t:a)v1.push_back(t);
    for(auto t:b)v1.push_back(make_pair(t.first,N+wz[t.second]));
    v3.clear();
    for(auto t:b)v3.push_back(t);
    for(auto t:a)v3.push_back(make_pair(t.first,N+wz[t.second]));
    for(int t:nl)nd.push_back(t);
    for(int i=1;i<=s;i++)nd.push_back(N+i);
    N+=s;s=nr.size();
    for(int i=1;i<=s;i++)fr[N+i]=-1,wz[nr[i-1]]=i;
    for(int i=1;i<=s;i++)
    {
        int u=nr[i-1];
        for(int j=fr[u];j!=-1;j=ne[j])
            addb(N+wz[v[j]],N+i,w[j]);
    }
    for(auto t:d)v2.push_back(t);
    for(auto t:c)v2.push_back(make_pair(t.first,N+wz[t.second]));
    v4.clear();
    for(auto t:c)v4.push_back(t);
    for(auto t:d)v4.push_back(make_pair(t.first,N+wz[t.second]));
    for(int t:nr)nd.push_back(t);
    for(int i=1;i<=s;i++)nd.push_back(N+i);
    N+=s;
    int s1=v1.size(),s2=v2.size();
    /*for(int i=1;i<=s1+s2;i++)fr[N+i]=-1;
    for(int i=1;i<=s1;i++)
        addb(v3[i-1].second,N+i,0);
    for(int i=1;i<=s2;i++)
        addb(N+s1+i,v4[i-1].second,0);*/
    for(int i=1;i<=s1;i++)
    {
        for(int j=1;j<=s2;j++)
        {
            auto tl=v3[i-1],tr=v4[j-1];
            double c=di[tl.first][tr.first];
            addb(tl.second,tr.second,c);
        }
    }
    //for(int i=1;i<=s1+s2;i++)nd.push_back(N+i);
    //N+=s1+s2;
}
bool bk[MN];double jl[MN];int S,T;
double dij()
{
    for(int i=1;i<=N;i++)bk[i]=0,jl[i]=1e100;
    typedef pair<double,int> Pr;
    priority_queue<Pr,vector<Pr>,greater<Pr> >pq;
    pq.push(make_pair(0,S));jl[S]=0;
    while(pq.size())
    {
        auto t=pq.top();pq.pop();
        int u=t.second;
        if(u==T)return jl[u];
        if(bk[u])continue;
        bk[u]=1;
        for(int i=fr[u];i!=-1;i=ne[i])
        {
            double s=jl[u]+w[i];
            if(s<jl[v[i]])
            {
                jl[v[i]]=s;
                pq.push(make_pair(s,v[i]));
            }
        }
    }
    return -1;
}
double dfs(int u)
{
    //printf("u=%d\n",u);
    if(u==T)return 0;
    if(bk[u])return jl[u];
    double mi=1e100;
    for(int i=fr[u];i!=-1;i=ne[i])
    {
        double t=w[i]+dfs(v[i]);
        if(t<mi)mi=t;
    }
    bk[u]=1;
    return jl[u]=mi;
}
int main()
{
    //printf("%d",cal(2));
    int n;
    scanf("%d",&n);
    //for(int i=1;i<=100;i++)fr[i]=-1;
    for(int i=0;i<n;i++)
    {
        //X[i]=i;Y[i]=i;
        scanf("%d%d",&X[i],&Y[i]);
        sz[i].x=X[i];sz[i].y=Y[i];sz[i].i=i;
    }
    for(int i=0;i<n;i++)
        for(int j=0;j<n;j++)
            di[i][j]=dis(X[i]-X[j],Y[i]-Y[j]);
    vector<pair<int,int> >v1,v2;vector<int> nd;
    dfs(0,n-1,v1,v2,nd);
    S=N+1;T=N+2;fr[S]=fr[T]=-1;N+=2;
    
    for(auto t:v1)addb(S,t.second,0);
    for(auto t:v2)addb(t.second,T,0);
    //printf("N=%d bs=%d\n",N,bs);
    //double ans=dij();
    double ans=dfs(S);
    printf("%.10lf",ans);
    //printf("[%d]",n);
    //for(int i=1;i<=N;i++)printf("[%d]\n",fr[i]);
    return 0;
}