#include <iostream>
#include <queue>
#include <map>
#include <list>
#include <vector>
#include <string>
#include <limits>
#include <cassert>
#include <fstream>
#include <cstring>
#include <bitset>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstdio>
#include <ciso646>
#include <array>

using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

#define inf 0x3f3f3f3f
#define CLEAR(a) a = decltype(a)()
#define MP make_pair
#define ALL(a) (a).begin(),(a).end()
#define pii pair<int ,int>
#define pcc pair<char,char>
#define pic pair<int,char>
#define pci pair<char,int>
#define VS vector<string>
#define VI vector<int>
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define pi 2*acos(0.0)
#define INFILE() freopen("in.txt","r",stdin)
#define OUTFILE() freopen("out.txt","w",stdout)
#define ll long long
#define ull unsigned long long
#define eps 1e-14

struct edge {
	int to;
	int c;
	edge(int t_, int c_):to(t_), c(c_){}
	edge():to(0), c(0){}
};

int main(void) {
	int N, M, K; cin >> N >> M >> K;
	vector<vector<edge> > e(N+1);
	vector<int> d(K);
	REP(i, M) {
		int a, b, c; cin >> a >> b >> c;
		--a; --b;
		e[a].emplace_back(b, c);
		e[b].emplace_back(a, c);
	}
	for (auto &a : d) cin >> a;

	queue<int> que;
	for (int i = 0; i < N; ++i) que.push(i);
	queue<int> next;
	
	REP(k, K) {
		while (not que.empty()) {
			int node = que.front(); que.pop();
			for (auto &a : e[node]) {
				if (a.c == d[k]) next.push(a.to);
			}
		}
		swap(que, next);
	}

	cout << que.size() << endl;
	vector<int> res;
	while (not que.empty()) {
		res.push_back(que.front());
		que.pop();
	}
	sort(ALL(res));
	REP(i, res.size()) {
		cout << res[i] << (i == res.size() - 1 ? "\n" : " ");
	}

	return 0;
}