#include <cstdio>#include <cstring>#include <cmath>#include <queue>#include <stack>#include <vector>#include <string>#include <map>#include <set>#include <sstream>#include <iostream>#include <algorithm>#include <fstream>using namespace std;typedef long long ll;const double inf=1000000000.0;const int N=405;const int mod=1007;const double eps=1e-16;struct Edge { int b,c,nxt; double w;}e[99999];int n,m;int p[N];int cnt;struct point { double x,y;}pt[N];int pre[N],path[N];double dis[N];bool vis[N];bool spfa(int s,int t,int n) { int i,u; queue<int>q; for(i=1;i<=n;i++) dis[i]=inf+0.0; memset(vis,0,sizeof(bool)*(n+1)); dis[s]=0; q.push(s); while(!q.empty()) { u=q.front(); q.pop(); vis[u]=0; for(i=p[u];i!=-1;i=e[i].nxt) { int v=e[i].b; int c=e[i].c; double w=e[i].w; if(c>0&&dis[v]>dis[u]+w) { dis[v]=dis[u]+w; pre[v]=u , path[v]=i; if(!vis[v]) q.push(v),vis[v]=1; } } } if(dis[t]+eps>=inf) return 0; return 1;}double mfmc(int s,int t,int n) { int i; int aug,maxflow=0; double maxcost=0; while(spfa(s,t,n)) { aug=inf; for(i=t;i!=s;i=pre[i]) if(aug>e[path[i]].c) aug=e[path[i]].c; for(i=t;i!=s;i=pre[i]) e[ path[i] ].c-=aug , e[ path[i]^1 ].c+=aug; maxcost+=dis[t]*aug; maxflow+=aug; } return maxcost;}void addedge(int a,int b,int c,double w) { e[cnt].b=b; e[cnt].c=c; e[cnt].w=w; e[cnt].nxt=p[a]; p[a]=cnt++; e[cnt].b=a; e[cnt].c=0; e[cnt].w=-w; e[cnt].nxt=p[b]; p[b]=cnt++;}void init() { memset(p,-1,sizeof(p)); cnt=0;}int main(){ int i,j,t,cas=0; while(scanf("%d",&n)!=EOF) { init(); for(i=1;i<=n;i++) scanf("%lf%lf",&pt[i].x,&pt[i].y); for(i=1;i<=n;i++) { for(j=i+1;j<=n;j++) { double w=sqrt((pt[i].x-pt[j].x)*(pt[i].x-pt[j].x)+(pt[i].y-pt[j].y)*(pt[i].y-pt[j].y)); addedge(i+n,j,1,w); } addedge(i,i+n,1,-inf); if(i==1||i==n) addedge(i,i+n,1,0.0); } double ret=mfmc(1,n+n,n+n); printf("%.2fn",ret+n*inf); } return 0;}
