#include <iostream>
#include <cstring>
#include <algorithm>
#include <limits.h>
#include <cmath>
#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
/* ここからが本編 */
/*  */

int N,M,K;
int a[1000];
int b[1000];
int c[1000];
int d[1000];
int town[101] = {0};
int town_n = 0;
int target;
void town_search(int before,int i,int j)
{
  int k,l;
  int cnt = 0;
  if(j == K) {
    town[target] = 1;
    town_n++;
    return ;
  }
  for(k=0;k<M;k++) {
    if(d[K-1-j] == c[k] && before == b[k]) {
      town_search(a[k],i,j+1);
    }
  }
  for(k=0;k<M;k++) {
    if(d[K-1-j] == c[k] && before == a[k]) {
      town_search(a[k],i,j+1);
    }
  }
}
int main(void)
{
  int test = 1;
  int i,j,k,l;
  cin >> N >> M >> K;
  rep(i,M) {
    scanf("%d %d %d",&a[i],&b[i],&c[i]);
    if(a[i] < b[i]) swap(a[i],b[i]);
    // a[i] >= b[i] になる
  }
  rep(i,K) {
    scanf("%d",&d[i]);
  }
  for(i=0;i<M;i++) {
    if(c[i] != d[K-1]) continue;
    target = b[i];
    town_search(a[i],i,1);
    target = a[i];
    town_search(b[i],i,1);
  }
  cout << town_n << endl;
  
  for(i=1;i<N+1;i++) {
    if(town[i]) {
      printf("%d",i);break;
    }
  }

  for(i++;i<N+1;i++) {
    if(town[i]) printf(" %d",i);
  }
  cout << endl;
  return 0;
}