#include <bits/stdc++.h>
using namespace std;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FORR(x,arr) for(auto&& x:arr)
#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define RFOR(i,a,b) for (int i = (b)-1; i >= (a); i--)
#define REP(i,n) for (int i = 0; i < (n); i++)
#define RREP(i,n) for (int i = (n)-1; i >= 0; i--)
#define ALL(x) (x).begin(), (x).end()
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define RITR(x,c) for(__typeof(c.rbegin()) x=c.rbegin();x!=c.rend();x++)
#define BIT(n) (1LL<<(n))
#define SZ(x) ((int)(x).size())
typedef long long ll;
// -------------------------------------

int n, m, k;
typedef pair<int, int> II;
map<int, vector<II>> E;
int d[1000];

void out(set<int>& s) {
  int i = 0;
  int size = s.size();
  for (auto&&c : s) {
    printf(i + 1 < size ? "%d " : "%d\n", c);
    i++;
  }
}

void Main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> m >> k;
  REP(i, m) {
    int a, b, c;
    cin >> a >> b >> c;
    E[c].push_back({a, b});
  }
  REP(i, k) cin >> d[i];

  set<int> cur;
  set<int> nex;
  FOR(i, 1, n+1) cur.insert(i);

  REP(i, k) {
    nex.clear();
    FORR(ab, E[d[i]]) {
      int a = ab.first;
      int b = ab.second;
      if (cur.count(a)) nex.insert(b);
      if (cur.count(b)) nex.insert(a);
    }
    cur = nex;
  }

  cout << SZ(cur) << endl;
  out(cur);
}

int main() {Main(); return 0;}