#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;
int main() {
	bool now[500], nex[500];
	for (int i = 0; i < 500; i++) {
		now[i] = 1;
		nex[i] = 0;
	}
	int n, m, k;//n町ｍ道路ｋ料金個数；
	cin >> n >> m >> k;
	vector<int>a(m);
	vector<int>b(m);
	vector<int>c(m);
	vector<int>d(k);
	for (int i = 0; i < m; i++) {
		cin >> a[i] >> b[i] >> 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 w = 0; w < n; w++) {
			now[w] = nex[w];
			nex[w] = 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;
}