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

template<typename T>
istream &operator>>(istream &is,vector<T> &a){
    for(auto &v : a) cin >> v;
    return is;
}
template<typename T>
ostream &operator<<(ostream &os,const vector<T> &a){
    if(a.size() == 0) return os;
    cout << a.at(0);
    for(int i=1; i<a.size(); i++) cout << " " << a.at(i);
    cout << "\n";
    return os;
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,M,K; cin >> N >> M >> K;
    map<int,vector<pair<int,int>>> Cs;
    while(M--){
        int a,b,c; cin >> a >> b >> c; a--,b--,c--;
        Cs[c].push_back({a,b});
    }
    
    vector<bool> OK(N,true);
    while(K--){
        int d; cin >> d; d--;
        vector<bool> next(N);
        for(auto [a,b] : Cs[d]){
            if(OK.at(b)) next.at(a) = true;
            if(OK.at(a)) next.at(b) = true;
        }
        swap(OK,next);
    }
    int ok = 0;
    for(int i=0; i<N; i++) ok += OK.at(i);
    cout << ok << "\n";
    for(int i=0; i<N; i++) if(OK.at(i)) cout << i+1 << (ok==1?"\n":" "),ok--;
}