#include<bits/stdc++.h>

using namespace std;

const int maxn = ;

int x[maxn],y[maxn];

double dp[maxn][maxn];

bool vis[maxn][maxn];

#define Squ(x) ((x)*(x))

inline double dist(int a,int b)

{

    return sqrt(Squ(x[a]-x[b])+Squ(y[a]-y[b]));

}

int n;

double dfs(int i,int j)

{

    if(vis[i][j]) return dp[i][j];

    vis[i][j] = true;

    if(i == n-){

        return dp[i][j] = dist(i,n)+dist(j,n);

    }

    return dp[i][j] = min(dfs(i+,i)+dist(j,i+),dfs(i+,j)+dist(i,i+));

}

int main()

{

   // freopen("in.txt","r",stdin);

    while(~scanf("%d",&n)){

        for(int i = ; i <= n; i++) scanf("%d%d",x+i,y+i);

        memset(vis,,sizeof(vis));

        double ans = dfs(,);

        printf("%.2lf\n",ans);

    }

    return ;

}