#include <bits/stdc++.h>
 
using namespace std;
 
#define REP(i,last) for (int i=0;i<last;i++)
#define prints(str) cout << str << " ";
#define printn(str) cout << str << endl;

typedef pair<int, int> p_ii;
typedef long long ll;

const int MAX_N = 100;
const int MAX_M = 1000;
const int MAX_K = 1000;
struct root {
  int a, b, c;
};
root roots[MAX_M];
int d[MAX_K];

int main(){
  roots[0].a = 12;
  int N, M, K;
  cin >> N >> M >> K;
  REP(i,M){
    cin >> roots[i].a >> roots[i].b >> roots[i].c;
    --roots[i].a;
    --roots[i].b;
  }

  REP(i,K){ cin >> d[i]; }

  bool candidate[N];
  fill(candidate, candidate+N, true);

  REP(i,K){
    int pay = d[i];
    bool new_candidate[N];

    REP(j,M){
      if (roots[j].c != pay) continue;
      new_candidate[roots[j].a] |= candidate[roots[j].b];
      new_candidate[roots[j].b] |= candidate[roots[j].a];
    }
    REP(i,N){
      candidate[i] = new_candidate[i];
    }
  }

  cout << count(candidate, candidate+N, true) << endl;

  REP(i,N){
    if (candidate[i]) {
      prints(i+1);
    }
  }
  cout << endl;
}