#include <bits/stdc++.h>
using namespace std;
#define GET_MACRO(a, b, c, NAME, ...) NAME
#define rep(...) GET_MACRO(__VA_ARGS__, rep3, rep2)(__VA_ARGS__)
#define rep2(i, a) rep3 (i, 0, a)
#define rep3(i, a, b) for (int i = (a); i < (b); i++)
#define repr(...) GET_MACRO(__VA_ARGS__, repr3, repr2)(__VA_ARGS__)
#define repr2(i, a) repr3 (i, 0, a)
#define repr3(i, a, b) for (int i = (b) - 1; i >= (a); i--)
template<class T1, class T2> inline bool chmin(T1 &a, T2 b) { return b < a && (a = b, true); }
template<class T1, class T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
using ll = long long;

int n, m, k;
bool dp[1111][111];

map<int, vector<pair<int, int>>> g;

int main() {
	cin >> n >> m >> k;
	rep (i, m) {
		int a, b, c;
		cin >> a >> b >> c;
		a--; b--;
		g[c].emplace_back(a, b);
	}

	vector<int> d(k);
	rep (i, k) cin >> d[i];

	rep (i, n) dp[0][i] = true;

	rep (i, k) {
		for (auto e : g[d[i]]) {
			int u, v;
			tie(u, v) = e;
			dp[i + 1][v] |= dp[i][u];
			dp[i + 1][u] |= dp[i][v];
		}
	}

	vector<int> ans;
	rep (i, n) if (dp[k][i]) ans.push_back(i + 1);

	cout << ans.size() << endl;
	rep (i, ans.size()) cout << ans[i] << " ";
	cout << endl;

	return 0;
}