#include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
#define valid(y,x,h,w) (0<=y&&y<h&&0<=x&&x<w)
#define tpl(...) make_tuple(__VA_ARGS__)
const int INF = 0x3f3f3f3f;
const double EPS = 1e-8;
const double PI = acos(-1);
typedef long long ll;
typedef pair<int,int> pii;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
template<class T>ostream&operator<<(ostream &o,const vector<T>&t){o<<'[';FOR(i,t){if(i!=t.begin())o<<',';o<<*i;}return o<<']';}
template<class S,class T>ostream&operator<<(ostream &o,const pair<S,T>&t){return o<<'('<<t.first<<','<<t.second<<')';}
template<int N,class Tp>void output(ostream&,const Tp&){}
template<int N,class Tp,class,class ...Ts>void output(ostream &o,const Tp&t){if(N)o<<',';o<<get<N>(t);output<N+1,Tp,Ts...>(o,t);}
template<class ...Ts>ostream&operator<<(ostream&o,const tuple<Ts...>&t){o<<'(';output<0,tuple<Ts...>,Ts...>(o,t);return o<<')';}
template<class T>void output(T t,char z=10){if(t<0)t=-t,putchar(45);int c[20];
int k=0;while(t)c[k++]=t%10,t/=10;for(k||(c[k++]=0);k;)putchar(c[--k]^48);putchar(z);}
template<class T>void outputs(T t){output(t);}
template<class S,class ...T>void outputs(S a,T...t){output(a,32);outputs(t...);}
template<class T>void output(T *a,int n){REP(i,n)cout<<a[i]<<(i!=n-1?',':'\n');}
template<class T>void output(T *a,int n,int m){REP(i,n)output(a[i],m);}
template<class T>bool input(T &t){int n=1,c;for(t=0;!isdigit(c=getchar())&&~c&&c-45;);
if(!~c)return 0;for(c-45&&(n=0,t=c^48);isdigit(c=getchar());)t=10*t+c-48;t=n?-t:t;return 1;}
template<class S,class ...T>bool input(S&a,T&...t){input(a);return input(t...);}
template<class T>bool inputs(T *a, int n) { REP(i,n) if(!input(a[i])) return 0; return 1;}

int dp[1001][100];
vector<pii> g[100];

int main() {
  int n,m,k;
  while(input(n,m,k)){
    REP(i,n) g[i].clear();
    REP(i,m) {
      int a,b,c;
      input(a,b,c);
      a--;b--;
      g[a].push_back(pii(b,c));
      g[b].push_back(pii(a,c));
    }
    memset(dp,0,sizeof(dp));
    REP(i,100) dp[0][i] = 1;
    vector<int> d(k);
    REP(i,k) input(d[i]);
    REP(i,k) {
      REP(j,n) {
        if (!dp[i][j]) continue;
        FOR(it, g[j]) {
          if (it->second == d[i]) {
            dp[i+1][it->first] |= 1;
          }
        }
      }
    }
    vector<int> ans;
    REP(i,n) if (dp[k][i]) ans.push_back(i);
    cout << ans.size() << endl;
    REP(i,ans.size()) {
      printf("%d%c", ans[i]+1, i!=(int)ans.size()-1?' ':'\n');
    }
  }
}