C++ :

#include<iostream>
#include<math.h>
#include<stdio.h> 
//#include<fstream> 
using namespace std;
//ifstream fin("cin.in"); 

int n;
double f[1001][1001];
double d[1001][1001];
double x[1001],y[1001]; 

void Qsort(int left,int right){
     if(left>=right) return ;
     int i=left,j=right;double mid=x[(left+right)>>1];
     while(i<=j)
     {
       while(x[i]<mid) i++;
       while(x[j]>mid) j--;
       if(i<=j)
       {
         swap(x[i],x[j]);
         swap(y[i],y[j]);
         i++;j--; 
               } 
                } 
     Qsort(left,j);
     Qsort(i,right); 
     } 

int main()
{
    cin>>n;
    for(int i=1;i<=n;++i)
    cin>>x[i]>>y[i];
    
    Qsort(1,n); 
    
    for(int i=1;i<=n;++i)
    for(int j=i+1;j<=n;++j)
    d[i][j]=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
    
    for(int i=1;i<=n;++i)
    for(int j=1;j<=n;++j)
    f[i][j]=1e24;
     
    f[2][1]=d[1][2]; 
    for(int i=3;i<=n;++i)
    for(int j=1;j<i;++j)
    if(j+1<i) f[i][j]=f[i-1][j]+d[i-1][i];
    else
    {
      for(int k=1;k<j;++k)
      f[i][j]=min(f[i][j],f[j][k]+d[k][i]);   
        } 
             
    printf("%.2lf\n",f[n][n-1]+d[n-1][n]); 
    return 0; 
    
    }