#include <iostream>
#include <fstream>
#include <ctime>
#include <set>
#include <vector>
#include <cstdio>
#include <cmath>
using namespace std;

ifstream in("response.in");
#define cin in
//ofstream out("response.out");
//#define cout out

const double INF = 100000000.0;
int v, e, t, c, k, p;
double w[1001][1001], d[1001];
bool u[1001];

double dijkstra(int start)
{
	for (int j = 1; j <= v; j++)
	{
		d[j] = w[start][j];
		u[j] = false;
	}
	d[start] = 0;
	for (int j = 1; j < v; j++)
	{
		double minx = INF + 1.0;
		int tag;
		for (int r = 1; r <= v; r++)
			if (u[r] == false && d[r] < minx)
			{
				minx = d[r];
				tag = r;
			}
		if (tag == c)
			return d[tag];
		u[tag] = true;
		for (int r = 1; r <= v; r++)
			if (w[tag][r] + d[tag] < d[r])
				d[r] = w[tag][r] + d[tag];
	}
	return INF+1.0;
}


int main()
{
	cin >> v >> e >> t;
	for (int i = 1; i <= v; i++)
		for (int j = i + 1; j <= v; j++)
			w[i][j] = w[j][i] = INF;
	while (e--)
	{
		int a, b;
		cin >> a >> b;
		cin >> w[a][b];
	}
	for (int i = 1; i <= t; i++)
	{
		printf("Scenario %d:\n", i);
		cin >> c >> k;
		double minx = INF;
		for (int j = 0; j < k; j++)
		{
			double dis;
			cin >> p;
			if ((dis=dijkstra(p)) < minx)
				minx = dis;
		}
		if (fabs(minx-INF) < 0.0001)
			printf("Impossible.\n\n");
		else
			printf("%.2f\n\n", minx);
	}
	return 0;
}