#include <bits/stdc++.h>
using namespace std;
struct edge {
  int to, cost;
};

typedef vector< vector< edge > > Graph;

int N, M, K;
Graph graph;
int val[1000];
bool visited[100], dp[1000][1000];

void rec(int idx, int cnt)
{
  if(cnt == K) {
    visited[idx] = true;
  } else if(!dp[idx][cnt]++) {
    for(int i = 0; i < graph[idx].size(); i++) {
      edge& e = graph[idx][i];
      if(val[cnt] == e.cost) rec(e.to, cnt + 1);
    }
  }
}

int main()
{
  fill_n( *dp, 1000 * 1000, false);

  cin >> N >> M >> K;
  graph.resize(N);
  for(int i = 0; i < M; i++) {
    int a, b, c;
    cin >> a >> b >> c;
    --a, --b;
    graph[a].push_back((edge){b, c});
    graph[b].push_back((edge){a, c});
  }
  for(int i = 0; i < K; i++) {
    cin >> val[i];
  }
  for(int i = 0; i < N; i++) {
    for(int j = 0; j < graph[i].size(); j++) {
      edge&e = graph[i][j];
      if(val[0] == e.cost) rec(i, 1);
    }
  }
  cout << count(visited, visited + N, true) << endl;
  bool first = false;
  for(int i = 0; i < N; i++) {
    if(visited[i]) {
      if(first++) cout << " ";
      cout << i + 1;
    }
  }
  cout << endl;
}