bitonic tour luogu1523

#include<cstdio> 
#include<cstring>
#include<cmath>
#include<ctime>
#include<iostream>
#include<algorithm>
#include<queue>
#include<set>
#define inf (0x7fffffff)
#define l(a) ((a)<<1)
#define r(a) ((a)<<1|1)
#define b(a) (1<<(a))
#define T_min (1e-8)
#define R (0.9998)
#define e (2.718281828459045)
#define pi (3.14159265358979323846)
#define rep(i,a,b) for(int i=a;i<=(b);i++)
#define clr(a) memset(a,0,sizeof(a))
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
int readint(){
    int t=0,f=1;char c=getchar();
    while(!isdigit(c)){
        if(c=='-') f=-1;
        c=getchar();
    }
    while(isdigit(c)){
        t=(t<<3)+(t<<1)+c-'0';
        c=getchar();
    }
    return t*f;
}
const int maxn=1009;
int n;
double d[maxn][maxn];
struct node{
    double x,y;
    inline bool operator<(const node A)const{
        return x<A.x||(x==A.x&&y<A.y);
    }
}X[maxn];
double dis(int u,int v){
    return sqrt((X[u].x-X[v].x)*(X[u].x-X[v].x)+(X[u].y-X[v].y)*(X[u].y-X[v].y)); 
}
int main(){
    //freopen("#input.txt","r",stdin);
    //freopen("#output.txt","w",stdout);
    n=readint();
    rep(i,1,n){
        X[i].x=readint();X[i].y=readint();
    }
    sort(X+1,X+n+1);
    //rep(i,1,n) printf("%d %d
",X[i].x,X[i].y);
    rep(i,1,n) rep(j,1,n) d[i][j]=1e30;d[1][2]=dis(1,2);
    rep(j,2,n){
        rep(i,1,j-1){
            if(j==i+1){
                rep(k,1,i-1) d[i][j]=min(d[i][j],d[k][i]+dis(j,k));
            }else d[i][j]=min(d[i][j],d[i][j-1]+dis(j,j-1));
        }
    }
    double ans=1e30;
    rep(i,1,n-1) ans=min(ans,d[i][n]+dis(i,n));
    printf("%.2lf
",ans);
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}