#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using VI = vector<int>;
using VL = vector<ll>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define allpt(v) (v).begin(), (v).end()
#define allpt_c(v) (v).cbegin(), (v).cend()
#define allpt_r(v) (v).rbegin(), (v).rend()


const int mod = 1e9 + 7;
const string wsp = " ";
const string tb = "\t";
const string rt = "\n";

template <typename T>
void show1dvec(vector<T> v)
{
    if (v.size() == 0)
        return;
    int n = v.size() - 1;
    rep(i, n) cout << v[i] << wsp;
    cout << v[n] << rt;
    return;
}

template <typename T>
void show2dvec(vector<vector<T>> v)
{
    int n = v.size();
    rep(i, n) show1dvec(v[i]);
}

int main()
{

#ifdef DEBUG
    cout << "DEBUG MODE" << endl;
    ifstream in("input.txt"); //for debug
    cin.rdbuf(in.rdbuf());    //for debug
#endif

    const int maxpayment = 1001;
    int n, m, k, a, b, c, d;
    cin >> n >> m >> k;
    map<int, set<PII>> roadmap;
    set<int> candidate, next_candidate;
    VI ans;

    rep(i, n) candidate.insert(i + 1);
    rep(i, m)
    {
        cin >> a >> b >> c;
        roadmap[c].insert(make_pair(a, b));
        roadmap[c].insert(make_pair(b, a));
    }

    rep(i, k)
    {
        cin >> d;
        for (auto z : roadmap[d])
        {
            if (find(allpt(candidate), z.first) != candidate.cend())
                next_candidate.insert(z.second);
        }

        candidate.clear();
        candidate = next_candidate;
        next_candidate.clear();
    }
    for (int z : candidate)
        ans.push_back(z);
    
    cout << ans.size() << rt;
    show1dvec(ans);

    return 0;
}