#include <cstdio>
#include <vector>
#include <tuple>

typedef std::tuple<int,int,int> T;

int N, M, K;
std::vector<T> es;
int d[1000];
bool used[2][101];

int main(){
    scanf("%d %d %d", &N, &M, &K);

    for(int i=0;i<M;i++){
        int a, b, c;
        scanf("%d %d %d", &a, &b, &c);

        es.push_back(std::make_tuple(a, b, c));
    }

    for(int i=0;i<K;i++){
        scanf("%d", d+i);
    }

    for(const T& t : es){
        if(std::get<2>(t) == d[0]){
            used[0][std::get<0>(t)] = true;
            used[0][std::get<1>(t)] = true;
        }
    }

    int prev = 0, next = 1;
    for(int i=1;i<K;i++){
        for(int j=1;j<=N;j++){used[next][j] = false;}

        for(const T& t : es){
            if(std::get<2>(t) == d[i]){
                if(used[prev][std::get<0>(t)]){
                    used[next][std::get<1>(t)] = true;
                }
                if(used[prev][std::get<1>(t)]){
                    used[next][std::get<0>(t)] = true;
                }
            }
        }

        prev = !prev;
        next = !next;
    }

    std::vector<int> cs;
    for(int i=1;i<=N;i++){
        if(used[prev][i]){
            cs.push_back(i);
        }
    }

    printf("%d\n", cs.size());
    for(int i=0;i<cs.size();i++){
        printf("%d%c", cs[i], " \n"[i+1==cs.size()]);
    }
}