#include <bits/stdc++.h>
using namespace std;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))

int N,M,K;
map<int,vector<pair<int,int> >> m;

int main(){
    cin >>N>>M>>K;

    REP(i,M){
        int a,b,c;
        cin >> a >> b >> c;
        m[c].push_back(make_pair(a,b));
    }
    int d;
    set<int> s;
    cin >> d;
    for(auto it = m[d].begin(); it != m[d].end(); ++it){
        s.insert(it->first);
        s.insert(it->second);
    }
    REP(i,K-1){
        cin >> d;
        set<int> s2;
        for(auto it = m[d].begin(); it != m[d].end(); ++it){
            if(s.count(it->first)) s2.insert(it->second);
            if(s.count(it->second)) s2.insert(it->first);
        }
        s = move(s2);
    }
    vector<int> v;
    for(auto it = s.begin(); it != s.end(); ++it){
        v.push_back(*it);
    }
    cout << v.size() << endl;
    REP(i,v.size()-1){
        cout << v[i] << " ";
    }
    cout << v.back() << endl;
    return 0;
}