#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) for(int i = (n) - 1; (i) >= 0; --i)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD 1000007
#define INF 100000000
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PI;


int main() {
	int n, m, k;
	cin >> n >> m >> k;
	int a[1010], b[1010], c[1010];
	REP(i, m) cin >> a[i] >> b[i] >> c[i];
	int d[1010];
	REP(i, k) cin >> d[i];
	bool np[1010][101] = {};
	REP(i, n + 1) np[0][i] = true;
	REP(i, k) {
		REP(j, m) {
			if (d[i] == c[j] && np[i][a[j]]) np[i + 1][b[j]] = true;
			if (d[i] == c[j] && np[i][b[j]]) np[i + 1][a[j]] = true;
		}
	}
	set<int> st;
	FOR(i, 1, n + 1) {
		if (np[k][i]) st.insert(i);
	}
	cout << st.size() << endl;
	for (auto e : st) {
		cout << e << " ";
	}
	cout << endl;
	return 0;
}