Alg

#include <iostream>
#include <vector>
#include <math.h>

using namespace std;

const double MAX = 10000001;

int n, m, k, l;
vector<pair <int, int>> g;
vector<double> minimum;
vector<bool> used;

double distance(int a, int b){
    double x = g[a].first - g[b].first;
    double y = g[a].second - g[b].second;
    return sqrt(x*x + y*y);
}

int main() {

    cin >> n;
    minimum.resize(n); used.resize(n);
    for (int i = 0; i < n; i++){
        cin >> k >> l;
        g.push_back(make_pair(k, l));
    }

    for(int i = 0; i < n; i++){
        minimum[i] = MAX;
        used[i] = false;
    }
    minimum[0] = 0;

    double len = 0;
    for (int i = 0; i < n; i++){
        int v = -1;
        for (int j = 0; j < n; j++){
            if (!used[j] && ((v == -1) || (minimum[j] < minimum[v]))){
                v = j;
            }
        }
        used[v] = true;
        len += minimum[v];
        for (int j = 0; j < n; j++){
            double dist = distance(v, j);
            minimum[j] = min(dist, minimum[j]);
        }
    }
    cout << len;
}