#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <fstream>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>
#include <iterator>
#include <atcoder/all>

#include <bits/stdc++.h>


#define rep(i,n) for (int i = 0; i < (n); ++i)
using namespace atcoder;
using namespace std;
typedef long long int ll;
typedef modint998244353 mint;




ll gcd(ll a, ll b) {
    if (a < b)swap(a, b);
    if (b == 0)return a;

    return gcd(b, a % b);
}
int lcm(int a, int b) {
    return a * b / gcd(a, b);
}

/*
解説動画参考
解説ブログ参考

*/



int main()
{

    int Q;
    Q = 1;
    //cin >> Q;   

    
    while (Q--) {
        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];

        }

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

        vector<vector<int>>p(1005, vector<int>(110));
        for (int i = 0; i < m; i++) {
            if (d[0] == c[i]) {
                p[0][a[i]] = 1;
                p[0][b[i]] = 1;
            }
        }
        for (int i = 1; i < k; i++) {
            for (int j = 0; j < m; j++) {
                if (d[i] == c[j]) {
                    if (p[i - 1][a[j]])p[i][b[j]] = 1;
                    if (p[i - 1][b[j]])p[i][a[j]] = 1;
                }
            }
        }
        vector<int> ans;
        for (int i = 0; i <= n; i++) {
            if(p[k-1][i])ans.push_back(i);
        }
        
        cout << ans.size() << endl;
        for (int i = 0; i < ans.size(); i++) {
            cout << ans[i] << " ";
        }
        
    }

    return 0;
}