#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;

#define FOR(I,A,B) for(int I = (A); I < (B); ++I)

typedef pair<int, long long> P;

int main(){
  int n,m,k;
  cin >> n >> m >> k;
  vector<vector<P> > g(n+1);
  FOR(i,0,m){
    int a, b;
    long long c;
    cin >> a >> b >> c;
    g[a].push_back(P(b,c));
    g[b].push_back(P(a,c));
  }
  long long d[k];
  FOR(i,0,k){
    cin >> d[i];
  }
  bool dp[k+1][n+1];
  FOR(i,0,k+1){
    FOR(j,0,n+1){
      if(i == 0) dp[i][j] = true;
      else dp[i][j] = false;
    }
  }
  FOR(i,0,k){
    FOR(j,0,n+1){
      if(!dp[i][j]) continue;
      for(auto to : g[j]){
        if(to.second == d[i]){
          dp[i+1][to.first] = true;
        }
      }
    }
  }
  vector<int> ans;
  FOR(i,1,n+1){
    if(dp[k][i]){
      ans.push_back(i);
    }
  }
  cout << ans.size() << endl;
  FOR(i,0,ans.size()){
    printf("%d%c", ans[i], i == ans.size() - 1 ? '\n' : ' ');
  }
  return 0;
}