Algo10B

#include <fstream>
#include <vector>
#include <cmath>
#include <iomanip>

using namespace std;

double inf = 40000;

double SpanTree(const vector<pair<long long, long long>> &vert)
{
    double dist = 0;
    vector<int> used(vert.size(), 0);
    vector<double> mindist(vert.size(), inf);
    mindist[0] = 0;
    int v = 0;

    for (int i = 0; i < vert.size(); i++)
    {
        int minind = v;
        double tmp = inf;
        used[v] = 1;
        dist += mindist[v];

        for (int j = 0; j < vert.size(); j++)
        {
            if (!used[j])
            {
                double wayvj = sqrt(pow(vert[v].first - vert[j].first, 2) + pow(vert[v].second - vert[j].second, 2));

                if (wayvj < mindist[j])
                    mindist[j] = wayvj;
                if (mindist[j] < tmp)
                {
                    minind = j;
                    tmp = mindist[j];
                }
            }
        }
        v = minind;
    }


    return dist;
}

int main()
{
    ifstream fcin("spantree.in");
    ofstream fcout("spantree.out");

    int n;
    fcin >> n;

    vector<pair<long long, long long>> vert(n);

    for (int i = 0; i < n; i++)
        fcin >> vert[i].first >> vert[i].second;

    fcout << fixed << setprecision(6);
    fcout << SpanTree(vert);

    return 0;
}