#include <iostream>
using namespace std;

int N, M, K;
int a[101], b[101], c[101];
int d[1001];
bool nex[101];
bool now[101];

int main(void) {
  cin >> N >> M >> K;
  for (int i = 0; i < M; i++) {
    cin >> a[i] >> b[i] >> c[i];
    a[i]--; b[i]--;
  }
  for (int i = 0; i < K; i++) cin >> d[i];
  for (int i = 0; i < N; i++) {
    now[i]  = true;
    nex[i] = false;
  }

  for (int i = 0; i < K; i++) {
    for (int j = 0; j < M; j++) {
      if (c[j] != d[i]) continue;
      nex[a[j]] |= now[b[j]];
      nex[b[j]] |= now[a[j]];
    }
    for (int j = 0; j < N; j++) {
      now[j] = nex[j];
      nex[j] = false;
    }
  }

  int count = 0;
  for (int i = 0; i < N; i++) {
    if (now[i]) count++;
  }
  cout << count << endl;
  for (int i = 0; i < N; i++) {
    if (!now[i]) continue;
    if (--count) cout << i + 1 << " ";
    else cout << (i + 1) << endl;
  }
  return 0;
}