#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int N, M, K;
vector<pii> g[100];
bool dp[2][100];

int main() {
	cin >> N >> M >> K;
	REP(i, M) {
		int a, b, c;
		scanf("%d %d %d", &a, &b, &c);
		a--; b--;
		g[a].push_back(pii(b, c));
		g[b].push_back(pii(a, c));
	}
	
	memset(dp[0], -1, sizeof(dp[0]));
	
	REP(i, K) {
		int d;
		scanf("%d", &d);
		
		int now = i % 2;
		int next = !now;
		
		memset(dp[next], 0, sizeof(dp[next]));
		
		REP(j, N) if (dp[now][j]) {
			REP(k, g[j].size()) if (g[j][k].second == d) {
				dp[next][g[j][k].first] = true;
			}
		}
	}
	
	vector<int> ans;
	REP(i, N) if (dp[K % 2][i]) ans.push_back(i + 1);
	
	cout << ans.size() << endl;
	REP(i, ans.size()) printf("%d%c", ans[i], i == ans.size() - 1 ? '\n' : ' ');
	
	return 0;
}