#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
#define rep(i, n) REP(i, 0, n)
#define REP(i, s, e) for (int i = (s); i < (int)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for (int i = (int)(s - 1); i >= (int)(e); i--)
#define all(r) r.begin(), r.end()
#define rall(r) r.rbegin(), r.rend()

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;

template <typename T, typename U>
T chmax(T& a, const U& b) {
    if (a >= b) return false;
    a = b;
    return true;
}
template <typename T, typename U>
T chmin(T& a, const U& b) {
    if (a <= b) return false;
    a = b;
    return true;
}

void yes_no(bool f, string yes = "Yes", string no = "No") { cout << (f ? yes : no) << "\n"; }

void solve() {
    int n, m, k;
    cin >> n >> m >> k;
    using P = pair<ll, ll>;
    vector<vector<P>> es(n);
    rep(i, m) {
        int a, b, c;
        cin >> a >> b >> c;
        --a;
        --b;
        es[a].emplace_back(b, c);
        es[b].emplace_back(a, c);
    }
    vector<ll> d(k);
    rep(i, k) cin >> d[i];
    unordered_set<int> s;
    rep(i, n) s.emplace(i);
    rep(i, k) {
        unordered_set<int> t;
        for (auto&& cur : s) {
            for (auto&& [x, y] : es[cur]) {
                if (y == d[i]) t.emplace(x);
            }
        }
        swap(s, t);
    }
    vi v;
    for (auto&& x : s) v.emplace_back(x + 1);
    sort(all(v));
    cout << v.size() << '\n';
    rep(i, v.size()) cout << v[i] << (i + 1 == (int)v.size() ? '\n' : ' ');
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t = 1;
    // cin >> t;
    rep(ti, t) solve();
    return 0;
}