#include <iostream>
#include <vector>
#include <tuple>
#include <numeric>

using namespace std;

int main(){
    int N, M, K, a, b;
    long long c, d;

    cin >> N >> M >> K;

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

    bool dp[K+1][N+1];
    for(int i=0; i<K+1; i++){
        for(int j=0; j<N+1; j++){
        	dp[i][j] = false;
        }
    }
    
    for(int i=0; i<K; i++){
        cin >> d;
        for(int j=0; j<M; j++){
            if(i==0){
                if(d==get<2>(abc[j])){
                    dp[i][get<0>(abc[j])] = true;
                    dp[i][get<1>(abc[j])] = true;
                }
            }else{
                if(d==get<2>(abc[j])){
                    if(dp[i-1][get<0>(abc[j])]) dp[i][get<1>(abc[j])] = true;
                    if(dp[i-1][get<1>(abc[j])]) dp[i][get<0>(abc[j])] = true;
                }
            }
        }
    }

    cout << accumulate(dp[K-1], dp[K-1]+N+1, 0) << endl;

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

    return 0;
}