#include <cstdio>
#include <algorithm>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <string>
#include <string.h>
#include <cstdlib>
#include <ctime>
#include <cmath>
#include <map>
#include <set>
#include <iostream>
#include <sstream>
#include <numeric>
#include <cctype>
#include <bitset>
#define fi first
#define se second
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define gep(i,g,j) for(int i = g.head[j]; i != -1; i = g.e[i].next)
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define rng(a) a.begin(),a.end()
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcount
#define snuke srand((unsigned)clock()+(unsigned)time(NULL));
#define df(x) int x = in()
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
inline int in() { int x; scanf("%d",&x); return x;}
inline void priv(vi a) { rep(i,sz(a)) printf("%d%c",a[i],i==sz(a)-1?'\n':' ');}

const int MX = 100005, INF = 1001001001;
const ll LINF = 1e18;
const double eps = 1e-10;

int n, m, k;
vvi to, co;

int dp[2][105];
map<int,vector<P>> e;

int main() {
  scanf("%d%d%d",&n,&m,&k);
  to = co = vvi(n);
  rep(i,m) {
    int a, b, c;
    scanf("%d%d%d",&a,&b,&c);
    --a; --b;
    e[c].pb(P(a,b));
  }
  rep(i,n) dp[0][i] = 1;
  int o = 0, p = 1;
  rep(ki,k) {
    int d;
    scanf("%d",&d);
    rep(i,n) dp[p][i] = 0;
    for (auto s : e[d]) {
      int a = s.fi;
      int b = s.se;
      dp[p][a] |= dp[o][b];
      dp[p][b] |= dp[o][a];
    }
    swap(o,p);
  }
  vi ans;
  rep(i,n) if (dp[o][i]) ans.pb(i+1);
  cout<<sz(ans)<<endl;
  priv(ans);
  return 0;
}