#include <iostream>
#include <vector>
#include <map>
#include <set>
using namespace std;

int main() {
    int N, M, K;
    cin >> N >> M >> K;

    vector<int> a(M), b(M), c(M);
    for (int i = 0; i < M; ++i) {
        cin >> a[i] >> b[i] >> c[i];
        --a[i], --b[i];
    }

    vector<int> d(K);
    for (int i = 0; i < K; ++i) cin >> d[i];

    vector<vector<bool>> dp(K, vector<bool>(N,false));
    for (int i = 0; i < M; ++i) {
        if (d[0] == c[i]) {
            dp[0][a[i]] = true;
            dp[0][b[i]] = true;
        }
    }

    for (int i = 1; i < K; ++i) {
        for (int j = 0; j < M; ++j) {
            if (d[i] == c[j]) {
                if (dp[i - 1][a[j]]) dp[i][b[j]] = true;
                if (dp[i - 1][b[j]]) dp[i][a[j]] = true;
            }
        }
    }

    int res = 0;
    for (int i = 0; i < N; ++i) {
        if (dp[K - 1][i]) ++res;
    }
    cout << res << endl;
    for (int i = 0; i < N; ++i) {
        if (dp[K - 1][i]) cout << i << " ";
    }
    cout << endl;
}