// No.92 逃走経路
// https://yukicoder.me/problems/no/92
//

#include <iostream>
#include <vector>
#include <unordered_set>
#include <algorithm>
using namespace std;


struct connection {
    int to;
    int cost;
};


vector<int> solve(unsigned int N, vector<vector<connection>> &cities, vector<int>& logs);

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    unsigned int N, M, K;
    cin >> N >> M >> K;

    vector<vector<connection>> cities(N+1);
    for (auto i = 0; i < M; ++i) {
        int a, b, c;
        cin >> a >> b >> c;
        cities[a].push_back(connection {b, c});
        cities[b].push_back(connection {a, c});
    }
    vector<int> logs(K);
    for (auto i = 0; i < K; ++i) {
        cin >> logs[i];
    }

    vector<int> ans = solve(N, cities, logs);
    cout << ans.size() << endl;
    for (int i = 0; i < ans.size(); ++i) {
        string s = (i+1 >= ans.size()) ? "\n": " ";
        cout << ans[i] << s;
    }
}

vector<int> solve(unsigned int N, vector<vector<connection>> &cities, vector<int>& logs) {
    unordered_set<int> possibilities;
    for (auto i = 1; i <= N; ++i)
        possibilities.insert(i);

    for (auto l: logs) {
        unordered_set<int> np;
        for (auto p: possibilities) {
            for (auto c: cities[p]) {
                if (c.cost == l)
                    np.insert(c.to);
            }
        }
        possibilities = move(np);
    }

    vector<int> ans;
    for (auto p: possibilities)
        ans.push_back(p);

    sort(ans.begin(), ans.end());
    return ans;
}