#define _CRT_SECURE_NO_WARNINGS
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#include <unordered_map>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii;
typedef long long ll; typedef vector<long long> vl; typedef pair<long long,long long> pll; typedef vector<pair<long long,long long> > vpll;
typedef vector<string> vs; typedef long double ld;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

int main() {
	int N, M, K;
	scanf("%d%d%d", &N, &M, &K);
	vector<vpii> g(N);
	rep(i, M) {
		int a, b, c;
		scanf("%d%d%d", &a, &b, &c), -- a, -- b;
		g[a].push_back(mp(b, c));
		g[b].push_back(mp(a, c));
	}
	vi d(K);
	rep(i, K) scanf("%d", &d[i]);
	vector<vector<bool> > dp(K+1, vector<bool>(N, false));
	rep(i, N) dp[0][i] = true;
	rep(k, K) {
		rep(i, N) if(dp[k][i]) {
			each(j, g[i]) if(d[k] == j->second)
				dp[k+1][j->first] = true;
		}
	}
	vi ans;
	rep(i, N) if(dp[K][i])
		ans.pb(i);
	cout << ans.size() << endl;
	each(i, ans) {
		if(i != ans.begin()) putchar(' ');
		printf("%d", *i + 1);
	}
	puts("");
	return 0;
}