#include <iostream>
#include <string>
#include <map>
#include <cmath>
#include <algorithm>
#include <vector>

using namespace std;
struct edge{
	int from,to,cost,num;
};
vector<vector<edge> >es;
vector<int> d;
vector<int> ans;
bool used[1010];

void dfs(int v,int k,int maxk){
	if(k == maxk){
		ans.push_back(v);
		return;
	}
	for(int i=0;i<es[v].size();i++){
		if(es[v][i].cost == d[k] && !used[es[v][i].num]){
			used[es[v][i].num] = true;
			dfs(es[v][i].to,k+1,maxk);
			used[es[v][i].num] = false;
		}
	}
}

int main(void){
	int n,m,k;
	cin >> n >> m >> k;
	es.resize(n);
	for(int i=0;i<m;i++){
		int a,b,c;
		cin >> a >> b >> c;
		a--;b--;
		es[a].push_back((edge){a,b,c,i});
		es[b].push_back((edge){b,a,c,i});
	}
	d.resize(k);
	for(int i=0;i<k;i++){
		cin >> d[i];
	}

	for(int i=0;i<n;i++){
		dfs(i,0,k);
	}
	sort(ans.begin(),ans.end());
	vector<int> ret;
	int pre = -1;
	for(int i=0;i<ans.size();i++){
		if(ans[i] != pre){
			//cout << ans[i] << endl;
			pre = ans[i];
			ret.push_back(ans[i]);
		}
	}

	cout << ret.size() << endl;
	for(int i=0;i<ret.size();i++){
		cout << ret[i]+1;
		if(i != ret.size()-1)cout << " ";
	}
	cout << endl;
	return 0;
}