#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
//#include <utility>
#include <set>
#include <iostream>
//#include <memory>
#include <string>
#include <vector>
#include <algorithm>
//#include <functional>
#include <sstream>
//#include <deque>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
//#include <cctype>
#include <cstring>
//#include <ctime>
#include <iterator>
#include <bitset>
//#include <numeric>
//#include <list>
//#include <iomanip>

#if __cplusplus >= 201103L
#include <array>
#include <tuple>
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <forward_list>

#define cauto const auto&
#else

#endif

using namespace std;


namespace{
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}


#define reep(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) reep((i),0,(n))
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define F first
#define S second
#define mkp make_pair
#define RALL(v) (v).rbegin(),(v).rend()


#define MOD 1000000007LL
#define EPS 1e-8
static const int INF=1<<24;
int n,m,K;
vint ans;
VV(pii) v;
vint ke;
int dp[110][1010];
int dfs(int x,int c){
	if(dp[x][c]) return 1;
	if(c==K){
		// cout<<x<<endl;
		ans.PB(x);
		return dp[x][c]=1;
	}
	int ret=0;
	rep(i,v[x].size()){
		if(v[x][i].S==ke[c]){
			ret=max(ret,dfs(v[x][i].F,c+1));
		}
	}
	return dp[x][c]=ret;
}

void mainmain(){
	cin>>n>>m>>K;
	v=VV(pii)(n);
	ke=vint(K);
	rep(i,m){
		int a,b,c;
		cin>>a>>b>>c;
		v[a-1].PB(mkp(b-1,c));
		v[b-1].PB(mkp(a-1,c));
	}
	rep(i,K) cin>>ke[i];
	// vint ans;
	rep(i,n){
		// cout<<"i "<<i<<endl;
		dfs(i,0);
	}
	sort(ALL(ans));
	ans.erase(unique(ALL(ans)),ans.end());
	cout<<ans.size()<<endl;
	rep(i,ans.size()){
		if(i) cout<<" ";
		cout<<ans[i]+1;
	}
	cout<<endl;
}



}
main() try{
    mainmain();
}
catch(...){
}