#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
using namespace std;

int main()
{
	int n, m, k;
	cin >> n >> m >> k;
	vector<int> a, b;
	vector<long> c;
	a.resize(m);
	b.resize(m);
	c.resize(m);
	for (int i = 0; i < m; i++){
		cin >> a[i] >> b[i] >> c[i];
	}

	vector<long> waru;
	waru.resize(k);
	vector<int> kouho;

	cin >> waru[0];
	for (int i = 0; i < m; i++){
		if (c[i] == waru[0]){
			kouho.push_back(a[i]);
			kouho.push_back(b[i]);
		}
	}
	for (int j = 1; j<k; j++){
		cin >> waru[j];
		for (int i = 0; i < m; i++){
			if (c[i] == waru[j]){
				int cnt = 0;
				for (int h = 0; h < kouho.size(); h++){
					if (kouho[h] == a[i]){

						if (!count(kouho.begin(), kouho.end(), b[i])){
							kouho.erase(kouho.begin() + h);
							kouho.push_back(b[i]);
							cnt++;
						}
					}
					else if (kouho[h] == b[i]){
						if (!count(kouho.begin(), kouho.end(), a[i])){
							kouho.erase(kouho.begin() + h);
							kouho.push_back(a[i]);
							cnt++;
						}
					}
				}
				if (cnt){
					kouho.erase(kouho.begin());
				}
			}
		}
		sort(kouho.begin(), kouho.end());
		unique(kouho.begin(), kouho.end());
	}

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