#include <iostream>
using namespace std;

int main(){
	int n, m, k;
	cin >> n >> m >> k;
	int a[m], b[m], c[m], d[k];
	for(int i = 0; i < m; i++){
		cin >> a[i] >> b[i] >> c[i];
		a[i]--;
		b[i]--;
	}
	for(int &i:d) cin >> i;
	bool dp[2][n];
	for(int i = 0; i < n; i++) dp[0][i] = true;
	for(int i = 0; i < k; i++){
		int now = i % 2, next = 1 ^ now;
		for(int j = 0; j < n; j++) dp[next][j] = false;
		for(int j = 0; j < m; j++){
			if(c[j] != d[i]) continue;
			dp[next][a[j]] |= dp[now][b[j]];
			dp[next][b[j]] |= dp[now][a[j]];
		}
	}
	int count = 0;
	for(int i = 0; i < n; i++) if(dp[k % 2][i]) count++;
	cout << count << endl;
	for(int i = 0; i < n; i++) if(dp[k % 2][i]) cout << i + 1 << ' ';
	cout << endl;
}