#include <unordered_map>
#include <string>
#include <vector>
#include <iostream>
#include <set>
#include <queue>
#include "optimization.h"
#include <math.h>
#include <unordered_map>
#include <iomanip>

using namespace std;
struct town {
    int x;
    int y;
};




int main() {
    vector<tuple<double, int, int>> edges;
    cout.tie(0);
    cin.tie(0);
    ios_base::sync_with_stdio(0);
    int n = readInt();
//    cin >> n;
    vector<town> towns(n);

    for (int i = 0; i < n; i++) {
//        cin >> towns[i].x >> towns[i].y;
        towns[i].x = readInt(); towns[i].y = readInt();

    }

    double answer = 0;
    vector<int> dist(n, INT32_MAX);
    dist[0] = 0;
    vector<bool> mark(n, false);
    for (int i = 0; i < n; i++){
        int cur_v = -1;
        for (int j = 0; j < n; j++){
            if (!mark[j] && (cur_v == -1 || dist[j] < dist[cur_v])) cur_v = j;
        }
        answer += sqrt(dist[cur_v]);
        mark[cur_v] = true;
        for (int k =0; k < n; k++){
            if (!mark[k]){
                dist[k] = min(dist[k], (towns[k].x - towns[cur_v].x) * (towns[k].x - towns[cur_v].x) + (towns[k].y - towns[cur_v].y) * (towns[k].y - towns[cur_v].y));
            }
        }
    }
//    cout << std::setprecision(10) << answer;
    writeDouble(answer, 10);
}