/* -*- coding: utf-8 -*-
 *
 * 92.cc: No.92 逃走経路 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100;
const int MAX_M = 1000;
const int MAX_K = 1000;

/* typedef */

typedef pair<int,int> pii;
typedef vector<pii> vpii;
typedef set<int> si;

/* global variables */

int n, m, k;
int as[MAX_M], bs[MAX_M], cs[MAX_M], ds[MAX_K];
vpii nbrs[MAX_N];
si ps[2];

/* subroutines */

/* main */

int main() {
  cin >> n >> m >> k;

  for (int i = 0; i < m; i++) {
    cin >> as[i] >> bs[i] >> cs[i];
    as[i]--, bs[i]--;
    nbrs[as[i]].push_back(pii(bs[i], cs[i]));
    nbrs[bs[i]].push_back(pii(as[i], cs[i]));
  }

  for (int i = 0; i < k; i++) cin >> ds[i];

  for (int i = 0; i < m; i++)
    if (cs[i] == ds[0]) {
      ps[0].insert(as[i]);
      ps[0].insert(bs[i]);
    }

  int cur = 0, nxt = 1;

  for (int i = 1; i < k; i++) {
    si &p0 = ps[cur], &p1 = ps[nxt];
    p1.clear();
    for (si::iterator sit = p0.begin(); sit != p0.end(); sit++) {
      vpii& nbru = nbrs[*sit];
      for (vpii::iterator vit = nbru.begin(); vit != nbru.end(); vit++) {
	int &v = vit->first, &c = vit->second;
	if (c == ds[i]) p1.insert(v);
      }
    }

    cur ^= 1, nxt ^= 1;
  }

  si &pc = ps[cur];
  printf("%lu\n", pc.size());

  bool first = true;
  for (si::iterator sit = pc.begin(); sit != pc.end(); sit++) {
    if (! first) putchar(' ');
    printf("%d", *sit + 1);
    first = false;
  }
  putchar('\n');

  return 0;
}