#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=l;i<r;i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=(r)-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[8]={1,0,-1,0,1,1,-1,-1};
const ll dx[8]={0,-1,0,1,1,-1,1,-1};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

int main(){
  ll n,m,k;cin >> n >> m >>k;
  vvpl g(n);
  rep(i,m){
    ll a,b,c;cin >> a >> b >> c;a--;b--;
    g[a].pb({b,c});
    g[b].pb({a,c});
  }
  vl d(k);rep(i,k)cin >> d[i];
  set<ll> st,nst;
  rep(i,n)st.ins(i);
  rep(j,k){
    for(auto v:st){
      for(auto p:g[v]){
        if(p.se==d[j])nst.insert(p.fi);
      }
    }
    st=nst;nst.clear();
  }
  cout << st.size() <<endl;
  for(auto p:st)cout << p+1 <<" ";cout << endl;
}