#include <bits/stdc++.h>
using namespace std;
template<typename type1,typename type2>
type2 vector_reduce(vector<type1>& v,function<type2(type2,type1)> fn,type2 initial){
    int N=v.size();
    type2 ans=initial;
    for(int i=0;i<N;i++){
        ans=fn(ans,v[i]);
    }
    return ans;
}
int main(){
    int N,M,K;
    cin>>N>>M>>K;
    vector<vector<int>> road(0,vector<int>(3));
    vector<bool> possible(N+1,true);
    vector<bool> next(N+1);
    vector<bool> mask(N+1);
    possible[0]=false;
    int a,b,c,d;
    for(int i=0;i<M;i++){
        cin>>a>>b>>c;
        road.push_back({a,b,c});
        road.push_back({b,a,c});
    }
    for(int i=0;i<K;i++){
        cin>>d;
        next=mask;
        for(int j=0;j<2*M;j++){
            if(possible[road[j][0]] && d==road[j][2]){
                next[road[j][1]]=true;
            }
        }
        possible=next;
    }
    function<int(int,bool)> fn=[](int p,bool a){return p+(a?1:0);};
    cout<<vector_reduce(possible,fn,0)<<endl;
    for(int i=0;i<N;i++){
        if(possible[i]){
            cout<<i<<" ";
        }
    }
    
}