#include <iostream>
#include <cmath>
using namespace std;

const int INT_MAX = 100000000;

class Point
{
    public:
        int x = 0, y = 0;
        double len2p(const Point& B)
        {
            return sqrt((B.x - x) * (B.x - x) + (B.y - y) * (B.y - y));
        };
};

int main()
{
    freopen("spantree.in","r",stdin);
    freopen("spantree.out","w",stdout);
    int n, x, y;
    double res = 0;
    cin >> n;

    Point buff[n];
    int vis[n];
    double edges[n];

    for (int i = 0; i < n; i++)
    {
        cin >> x >> y;
        buff[i] = Point{x, y};
        vis[i] = 0;
        if (i > 0) edges[i] = buff[0].len2p(buff[i]);
    }
    vis[0] = 1;


    for (int j = 1; j < n; j++)
    {
        double minLen = INT_MAX;
        int help = 0;
        for(int i = 1; i < n; i++)
            if (edges[i] < minLen && !vis[i])
            {
                minLen = edges[i];
                help = i;
            }
        vis[help] = 1;
        res += minLen;
        for (int i = 0; i < n; i++)
        {
            if (!vis[i])
            {
                double len = buff[help].len2p(buff[i]);
                if (len < edges[i]) edges[i] = len;
            }
        }
    }
    cout << res << "\n";
    return 0;
}