#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <list>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <functional>
using namespace std;
typedef long long int llint;
const int INF = 1000000;
const llint LINF = 100000000;
//何番目
int black[10000] = { 0 }, bn, wn;
int white[10000] = { 0 };
llint dp[INF];
bool now[101];
bool nex[101];
int main() {
	for (int i = 0; i < 101; i++) {
		now[i] = 1;
		nex[i] = 0;
	}
	llint n, m, k;
	cin >> n >> m >> k;
	vector<llint>b(m);
	vector<llint>a(m);
	vector<llint>c(m);
	vector<llint>d(k);
	for (int i = 0; i < m; i++) {
		cin >> a[i];
		cin >> b[i];
		cin >> c[i];
		a[i]--;
		b[i]--;
	}
	for (int i = 0; i < k; i++) {
		cin >> d[i];
	}
	for (int i = 0; i < k; i++) {
		for (int j = 0; j < m; j++) {
			if (c[j] != d[i])continue;
			else {
				nex[a[j]] |= now[b[j]];
				nex[b[j]] |= now[a[j]];
			}
		}
			for (int j = 0; j < n; j++) {
				now[j] = nex[j];
				nex[j] = 0;
			}
		}
		int ans = 0;
		for (int i = 0; i < n; i++) {
			ans += now[i];
		}
		cout << ans << endl;
		for (int i = 0; i < n; i++) {
			if (now[i]) {
				if(--ans)cout << i + 1 << " ";
				else cout << i + 1 << endl;
			}
		}
			
			//cin >> n;
			return 0;
		}