#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

struct Path {
    int a;
    int b;
    long long c;
};

int main() {
    
    int N,M,K;
    cin >> N >> M >> K;
    
    vector< vector<int> > V( K+1, vector<int>( N, 0 ) );       
    Path P[1000];
    
    for ( int i = 0; i < N; i++ ) {
        V[0][i] = 1;
    }
    
    for ( int i = 0; i < M; i++ ) {
        cin >> P[i].a >> P[i].b >> P[i].c;
        P[i].a--; P[i].b--;
    }
    
    vector<long long> D(K);
    for ( int i = 0; i < K; i++ ) {
        cin >> D[i];
    }
    
    for ( int i = 1; i <= K; i++ ) {        
        long long d = D[i-1];        
        for ( int j = 0; j < M; j++ ) {
            if ( P[j].c == d ) {
                if ( V[i-1][P[j].a] ) { V[i][P[j].b] = 1; }
                if ( V[i-1][P[j].b] ) { V[i][P[j].a] = 1; }
            }
        }
    }
    
    vector<int> A;
    for ( int i = 0; i < N; i++ ) {
        if ( V[K][i] ) { A.push_back(i); }
    }
    
    cout << A.size() << endl;
    
    for ( int i = 0; i < A.size(); i++ ) {
        cout << A[i]+1;
        if ( i != A.size()-1 ) { cout << " "; }
    }
    cout << endl;
    
    return 0;
}