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

#define int long long

#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define pb push_back
#define all(v) (v).begin(),(v).end()
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;

int N,M,K;

int A[1000],B[1000],C[1000];

signed main(){
    cin>>N>>M>>K;
    rep(i,M)cin>>A[i]>>B[i]>>C[i],A[i]--,B[i]--;

    bool prev[100],next[100];
    fill_n(prev,N,true);

    while(K--){
        int d;cin>>d;
        rep(i,M)if(C[i]==d&&prev[A[i]])next[B[i]]=true;
        rep(i,M)if(C[i]==d&&prev[B[i]])next[A[i]]=true;
        rep(i,N)prev[i]=next[i];
        fill_n(next,N,false);
    }
    vint ans;
    rep(i,N)if(prev[i])ans.pb(i);
    cout<<ans.size()<<endl;
    rep(i,ans.size()){
        if(i)cout<<" ";
        cout<<ans[i]+1;
    }cout<<endl;
    return 0;
}