#include <bits/stdc++.h>
using namespace std;

// 基本テンプレート
struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;
#define P(x) cout << (x) << endl
#define p(x) cout << (x)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define mat(type, c, m, n) vector<vector<type>> c(m, vector<type>(n));for(auto& r:c)for(auto& i:r)cin>>i;
#define rep(i,a,n) for(int i=(a), i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,n) for(int i=(a); i>n; --i)
#define each(x,y) for(auto &(x):(y))
#define perm(c) sort(all(c));for(bool c##p=1;c##p;c##p=next_permutation(all(c)))
#define cauto const auto&
#define UNIQUE(v) v.erase( unique(all(v)), v.end() );
#define len(x) ((int)(x).size())
#define length(a)   (sizeof(a)/sizeof(a[0]))
template<typename T> inline bool inside(T y, T x, T h, T w) { return 0 <= y && y < h && 0 <= x && x < w; };

// デバッグ用
template <class T> inline void print(T t){cout << t << endl;}
template <class H, class... T> inline void print(H h, T... t){cout << h << " ";print(t...);}
#define dbg(v) for(auto i : v) { cout << i << " "; } cout << endl;

// 型
typedef long long ll;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<long long> vll;
typedef vector<string> vs;
typedef vector<bool> vb;



// 定数
#define PI acos(-1.0)
//constexpr int EPS = (1e-9);
//constexpr int INF = 100000000;

// 4近傍
//constexpr int dx[] = {1, 0, -1, 0};
//constexpr int dy[] = {0, 1, 0, -1};


// 8近傍
//constexpr int dy[]={0,0,1,-1,1,1,-1,-1};
//constexpr int dx[]={1,-1,0,0,1,-1,1,-1};

//constexpr int MAX = 1005;

//ll mod = 1000007;

int main() {
//	cout << setprecision(12) << fixed;

	int n, m, k; cin >> n >> m >> k;
	vector<unordered_map<int,vi>> g(n);
	rep (i, 0, m) {
	    int a, b, c; cin >> a >> b >> c; --a; --b;
	    g[a][c].push_back(b);
	    g[b][c].push_back(a);
	}
	vi ds(k); rep (i, 0, k) cin >> ds[i];
	unordered_set<int> xs; rep(i, 0, n) xs.insert(i);
	for(int d : ds) {
		unordered_set<int> ys;
		for(int x : xs) {
			if (g[x].count(d) == 0) continue;
			for (int y : g[x][d]) {
				ys.insert(y);
			}
		}
		xs = ys;
	}
	vi ans(all(xs));
	sort(all(ans));
	P(len(ans));
	rep(i, 0, len(ans)) cout << ans[i] + 1 << (i != len(ans) -1 ? " " : "\n");

	return 0;
}