#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <fstream>
#include <string>
#include <set>
#include <deque>
#include <queue>
#include <map>
#include <bitset>
#include <random>

using namespace std;

typedef int ll;
typedef unsigned long long ull;
typedef double ld;
#define endl "\n"

#define all(a) a.begin(), a.end();

const ll inf = 1e9;
long double eps = 1e-9;
const ll maxsz = 5001;
pair<ll, ll> a[maxsz];
vector <pair <ll, ld> > gr[maxsz];

ld getl(ll x1, ll y1, ll x2, ll y2) {
    return sqrt(((x1 - x2) * (x1 - x2)) + ((y1 - y2) * (y1 - y2)));
}

signed main() {
#ifdef _DEBUG
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cout.tie(NULL);
    ll n, i, j;
    cin >> n;
    for (i = 0; i < n; i++) {
        cin >> a[i].first >> a[i].second;
    }
    for (i = 0; i < n; i++) {
        for (j = i + 1; j < n; j++) {
            gr[i].push_back({ j,getl(a[i].first, a[i].second, a[j].first, a[j].second) });
            gr[j].push_back({ i,getl(a[i].first, a[i].second, a[j].first, a[j].second) });
        }
    }
    vector <ld> d(n, inf);
    vector <bool> used(n, false);
    d[0] = 0;
    ld ans = 0;
    for (i = 0; i < n; i++) {
        ll v = -1;
        for (ll u = 0; u < n; u++) {
            if (!used[u] && (v == -1 || d[v] > d[u])) {
                v = u;
            }
        }
        used[v] = true;
        ans += d[v];
        for (auto [u, w] : gr[v]) {
            if (d[u] > w) {
                d[u] = w;
            }
        }
    }
    cout << fixed << setprecision(10)
        << ans;
}