#include <bits/stdc++.h>
using namespace std;

#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
#define __fix ios_base::sync_with_stdio(0); cin.tie(0);

typedef long long LL;
typedef double LD;
typedef pair < int, int > PII;
typedef pair < LL, LL > PLL;
typedef pair < LD, LD > PDD;

typedef complex < double > CP;

const int N = 4 * (3e3 + 7);

int n;
CP T[N];
bool vis[N];
map < PDD, int > MP;
CP I(0, 1);

PDD con(const CP &c)
{
	return make_pair(real(c), imag(c));
}

bool cmp(const CP &c1, const CP &c2)
{
	return make_pair(real(c1), imag(c1)) < make_pair(real(c2), imag(c2));
}

int main()
{
	cin >> n;
	n *= 4;
	for(int i = 0; i < n; i++)
	{	
		int a, b;
		cin >> a >> b;
		T[i] = CP(a, b);
	}	
	sort(T, T + n, cmp);
	for(int i = 0; i < n; i++)
		MP[con(T[i])] = i;
	LD ans = 0;
	for(int i = 0; i < n; i++)
	{
		if(vis[i] == 1)
			continue;
		vis[i] = 1;
		for(int j = i + 1; j < n; j++)
		{
			if(vis[j]) continue;
			
			CP r = T[j] - T[i];
			CP a1 = T[i] + r * (I + 1.0) / 2.0;
			CP a2 = T[i] + r * (1.0 - I) / 2.0;
			if(MP.find(con(a1)) != MP.end() && MP.find(con(a2)) != MP.end())
			{
				int i1 = MP[con(a1)], i2 = MP[con(a2)];
				if(vis[i1] || vis[i2]) continue;
				ans += norm(T[i] - T[i1]);
				vis[i] = vis[j] = vis[i1] = vis[i2] = true;
				break;
			}
			
		}
	}
	cout << fixed << setprecision(12) << ans << "\n";
	return 0;
}