#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

bool dp[1010][110];

int main(){

  int n,m,k;
  cin >> n >> m >> k;

  vector<int> a(m),b(m),c(m);
  rep(i,m) cin >> a[i] >> b[i] >> c[i],--a[i],--b[i];

  vector<int> d(k);
  rep(i,k) cin >> d[i];

  rep(j,n) dp[0][j] = true;

  rep(i,k) {
    rep(j,m) {
      if (d[i] == c[j]) {
        dp[i+1][a[j]] |= dp[i][b[j]];
        dp[i+1][b[j]] |= dp[i][a[j]];
      }
    }
  }

  int res = 0;
  rep(j,n) if (dp[k][j]) res++;
  cout << res << endl;
  rep(j,n) if (dp[k][j]) cout << j+1 << " ";
  cout << endl;
  return 0;
}