#include<iostream>
#include<cstdio>
#include<cstdlib>
using namespace std;

const int maxm = 1000 + 10;
int m;
double time = 0.0;
double sl = 0.0;

struct node
{
	int u;
	int v;
	int len;
}r[maxm];

struct node2
{
	int s[maxm];
	int p;
}t[maxm];

int main()
{
	freopen("firelead.in","r",stdin);
	freopen("firelead.out","w",stdout);
	t[1].p = 0;
	cin >> m;
	for (int i = 1; i <= m; i++)
		cin >> r[i].u >> r[i].v >> r[i].len;
	bool b = true;
	for (int i = 1; i <= m; i++)
	{
		if (r[i].len != 1)
		{
			b = false;
			break;
		}
		else
			continue;
	}
	if(!b)
	{
		for (int i = 1; i <= m; i++)
		{
			sl += r[i].len;
		}
		time = sl / 4 * 3  / 2;
	}
	else
		time = 1;
	cout << time;
	return 0;
}