#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N, M, K;
    cin >> N >> M >> K;

    vector<map<ll, vector<ll> > > G(N);

    FOR(i, 0, M){
        ll a, b, c;
        cin >> a >> b >> c;
        a--;
        b--;

        G[a][c].push_back(b);
        G[b][c].push_back(a);
    }

    vector<ll> D(K);
    FOR(i, 0, K){
        cin >> D[i];
    }

    // candidates
    set<ll> se;
    FOR(i, 0, N){
        se.insert(i);
    }

    for(ll d : D){
        set<ll> se2;
        for(ll from : se){
            for(ll to : G[from][d]){
                se2.insert(to);
            }
        }
        se = se2;
    }

    p(se.size());
    for(ll a : se){
        cout << a+1 << " ";
    }
    cout << endl;
    
    return 0;
}