#include <bits/stdc++.h>

template<typename T> T in() { abort(); return T(); }
template<> std::string in() { std::string str; std::cin >> str; return str; }
template<> int in() { int x; scanf("%d", &x); return x; }

template<typename T> void out(T x) { abort(); }
template<> void out(const char* x) { printf("%s\n", x); }
template<> void out(std::string x) { std::cout << x << std::endl; }
template<> void out(int x) { printf("%d\n", x); }
template<> void out(long x) { printf("%ld\n", x); }
template<> void out(size_t x) { printf("%lu\n", x); }

struct Edge {
  Edge() {}
  Edge(int from_, int to_, int cost_) : from(from_), to(to_), cost(cost_) {}
  int from;
  int to;
  int cost;
}; 

int n, m, k;
Edge edge[1024];
int d[1024];

int main() {
  n = in<int>();
  m = in<int>();
  k = in<int>();
  for(int i = 0; i < m; ++i) {
    edge[i].from = in<int>();
    edge[i].to   = in<int>();
    edge[i].cost = in<int>();
  }
  for(int i = 0; i < k; ++i) {
    d[i] = in<int>();
  }

  bool flags[2][1024];
  bool *xs = flags[0];
  bool *ys = flags[1];

  for(int i = 1; i <= n; ++i) {
    xs[i] = true;
  }

  for(int i = 0; i < k; ++i) {
    for(int j = 1; j <= n; ++j) ys[j] = false;
    for(int j = 0; j < m; ++j) {
      int from = edge[j].from;
      int to   = edge[j].to;
      int cost = edge[j].cost;
      if( cost == d[i] ) {
        ys[to] = ys[to] or xs[from];
        ys[from] = ys[from] or xs[to];
      }
    }
    std::swap(xs, ys);
  }

  std::vector<int> res;
  for(int i = 1; i <= n; ++i) {
    if( xs[i] ) res.push_back(i);
  }

  out(res.size());
  printf("%d", res[0]);
  for(int i = 1; i < (int)res.size(); ++i) {
    printf(" %d", res[i]);
  }
  puts("");
  
  return 0;
}