I

    #include <iostream>
    #include <algorithm>
    #include <vector>
    #include <map>
    #include <cmath>

    typedef std::pair<int, int> point2d;
    typedef std::vector<int> iVec;

    std::vector<point2d> In;
    std::map<point2d, int> dist;
    std::map<int, int> min_e;
    std::vector<bool> used;

    int len( const point2d & A, const point2d & B ) { return (A.first - B.first) * (A.first - B.first) + (A.second - B.second) * (A.second - B.second); }

    std::pair<int, int> find_min( int a )
    {
      int lenn, min_l = -1, min_ind = -1;
      for (int b = 0; b < In.size(); b++)
      {
        if (a == b || used[b])
          continue;

        lenn = (!dist[{a, b}]) ? (dist[{a, b}] = dist[{b, a}] = len(In[a], In[b])) : dist[{a, b}];
        if ((lenn < min_l) || (min_l == -1))
          min_l = lenn, min_ind = b;
      }
      min_e[a] = min_ind + 1;
      return std::make_pair(min_ind, min_l);
    }

    int main()
    {
      int n = 0;
      scanf("%i", &n);
      int x = 0, y = 0, i, tmp = 1;
      long double res = 0;
      std::pair<int, int> best_p;
      used.resize(n);
      std::generate(used.begin(), used.end(), []() { return false; });
      int min_l = -1, min_ind = -1, lenn;

      // Prim
      i = n;
      while (i--)
        scanf("%i%i", &x, &y), In.push_back(point2d(x, y));

      // fill the mst
      used[0] = true;
      for (int size = n - 1; size; size--)
      {
        min_l = min_ind = -1;
        for (int a = 0; a < n; a++)
        {
          if (!used[a])
            continue;

          tmp = min_e[a] - 1;

          if (!min_e[a] || used[min_e[a] - 1])
            tmp = find_min(a).first;

          lenn = (!dist[{a, tmp}]) ? (dist[{a, tmp}] = dist[{tmp, a}] = len(In[a], In[tmp])) : dist[{a, tmp}];
          if ((lenn < min_l) || (min_l == -1))
            min_l = lenn, min_ind = tmp;
        }

        if (min_ind == -1)
        { printf("0");
        return 0; }

        used[min_ind] = true;
        res += sqrt(min_l);

        // recount if needed
        for (int a = 0; a < n; a++)
          if (used[a] && (!min_e[a] || used[min_e[a] - 1]))
            find_min(a);
      }

      //
      printf("%lf", res);

      return 0;
    }