#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

int N, M, K;
vector<pair<int, int>> es[100];
int d[1000];

int main(int argc, char **argv) {
	cin >> N >> M >> K;
	REP(i, M) {
		int a, b, c;
		cin >> a >> b >> c;
		--a; --b;
		es[a].push_back(MP(b, c));
		es[b].push_back(MP(a, c));
	}
	REP(i, K) cin >> d[i];
	set<int> q[2];
	int qi[2] = { 0, 1 };
	REP(i, N) q[qi[0]].insert(i);
	REP(i, K) {
		q[qi[1]].clear();
		for (auto it = q[qi[0]].begin(); it != q[qi[0]].end(); ++it) {
			REP(j, es[*it].size()) if (es[*it][j].second == d[i]) q[qi[1]].insert(es[*it][j].first);
		}
		swap(qi[0], qi[1]);
	}
	cout << q[qi[0]].size() << endl;
	for (auto it = q[qi[0]].begin(); it != q[qi[0]].end(); ++it) {
		if (it != q[qi[0]].begin()) cout << " ";
		cout << ((*it) + 1);
	}
	cout << endl;
	return 0;
}