#include <iostream>
#include <fstream>
#include <vector>
#include <limits>
#include <utility>
#include <queue>
#include <iomanip>
using namespace std;

double dias(const vector< vector<double> >& mmap, int s, int d)
{
	vector<double> rgf(mmap.size(), numeric_limits<double>::max());
	vector<bool> visited(mmap.size(), false);
	priority_queue< pair<double, int> > q;
	q.push(make_pair(0.0, s));
	while (!q.empty()) {
		int u=q.top().second;
		double f=-q.top().first;
		if (u==d)
			break;
		q.pop();
		visited[u]=true;
		for (int v=0; v<mmap[u].size(); ++v) {
			if (mmap[u][v]>=0 && visited[v]==false && f+mmap[u][v]<rgf[v]) {
				rgf[v]=f+mmap[u][v];
				q.push(make_pair(-rgf[v], v));
			}
		}
	}

	if (q.empty())
		return -1;
	else
		return -q.top().first;
}

int main(int, char**)
{
	ifstream ifile("response.in");
	int n, m, cs; ifile>>n>>m>>cs;
	vector< vector<double> > mmap(n, vector<double>(n, -1));
	for (int i=0; i<m; ++i) {
		int s, d;
		double dist;
		ifile>>s>>d>>dist;
		mmap[s-1][d-1]=dist;
	}

	for (int scenerio=1; scenerio<=cs; ++scenerio) {
		int d; ifile>>d;
		int k; ifile>>k;
		double ans=-1;
		for (int j=0; j<k; ++j) {
			int s; ifile>>s;
			const double dist = dias(mmap, s-1, d-1);
			//cout<<dist<<endl;
			if (ans<0 || dist<ans) {
				ans=dist;
			}
		}

		cout<<"Scenerio "<<scenerio<<':'<<endl;
		if (ans<0) {
			cout<<"Impossible."<<endl<<endl;
		}
		else {
			cout<<fixed<<setprecision(2)<<ans<<endl<<endl;
		}
	}
}