#include <bits/stdc++.h>
using namespace std;
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);  
	int n, m, k;
	cin >> n >> m >> k;
	vector<int> a(m), b(m), c(m);
	for(int i = 0; i < m; i++) {
		cin >> a[i] >> b[i] >> c[i];
		a[i]--; b[i]--;
	}
	vector<vector<int>> dp(k + 1, vector<int>(n));
	for(int i = 0; i < n; i++) {
		dp[0][i] = 1;
	}
	for(int i = 1; i <= k; i++) {
		int d;
		cin >> d;
		for(int j = 0; j < m; j++) {
			if(d == c[j]) {
				if(dp[i - 1][a[j]]) dp[i][b[j]] = 1;
				if(dp[i - 1][b[j]]) dp[i][a[j]] = 1;
			}
		}
	}
	cout << accumulate(dp[k].begin(), dp[k].end(), 0) << endl;
	for(int i = 0; i < n; i++) {
		if(dp[k][i]) cout << i  + 1 << " ";
	}
	cout << endl;
	return 0;
}