#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include <sstream>
#include<iomanip>

//#include<bits/stdc++.h>


using namespace std;
vector<int>g[1005];
int main() {

	int n, m, k;
	cin >> n >> m >> k;
	vector<pair<int, int>>x[102];
	for (int i = 0; i < m; i++) {
		int a, b, j;
		cin >> a >> b >> j;
		a--; b--;
		x[a].push_back(make_pair(j, b));
		x[b].push_back(make_pair(j, a));
	}
	
	for (int i = 0; i < n; i++) {
		g[0].push_back(i);
	}
	for (int i = 0; i < k; i++) {
		int d;
		cin >> d;
		for (int j = 0; j < g[i].size(); j++) {
			
			for (int w = 0;w< x[g[i][j]].size(); w++) {
				if (x[g[i][j]][w].first == d)g[i + 1].push_back(x[g[i][j]][w].second);
			}
		}
		
	}
	sort(g[k].begin(), g[k].end());
	cout << g[k].size() << endl;
	for (int i = 0; i < g[k].size(); i++) {
		if (i)cout << " ";
		cout << g[k][i]+1 ;
		if (i == g[k].size() - 1)cout << endl;
	}

	return 0;
}