#include<bits/stdc++.h>
#define f first
#define s second
#define sqr(a) ((a)*(a))
using namespace std;

#pragma pack(1)

int i, j, k, o, x, y, n, m, pr[5000+10], sz[5000+10];
long double ans;
struct my
{
    int x;
    int y;
    int d;
};
my b[1000000*15];
pair<int, int> a[5000+10];
inline int dist(int x, int y, int xx, int yy)
{
  int k=(sqr(x-xx)+sqr(y-yy));
    return k;
}
bool cmp(my a, my b)
{
    if (a.d<b.d) return true;
    return false;
}
int get(int v)
{
    if (v==pr[v]) return v;
    int res = get(pr[v]);
    pr[v] = res;
    return res;
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin>>n;
    for (i=1;i<=n;i++)
    {
        cin>>a[i].f>>a[i].s;
        pr[i]=i;
        sz[i]=0;
    }
    for (i=1;i<n;i++)
    {
        for (j=i+1;j<=n;j++)
        {
            int len=dist(a[i].f, a[i].s, a[j].f, a[j].s);
            m++;
            b[m].x=i;
            b[m].y=j;
            b[m].d=len;
        }
    }
    sort(b+1, b+m+1, cmp);

    for (i=1;i<=m;i++)
    {

        x=get(b[i].x);
        y=get(b[i].y);

        if (x!=y)
            {

                ans+=sqrt(sqr(a[b[i].x].f-a[b[i].y].f)+sqr(a[b[i].x].s-a[b[i].y].s));
               if (rand()&1) swap (x, y);
	            pr[x]=y;
            }


    }
    cout.precision(12);
    cout<<fixed;
    cout<<ans;
}