/*
    Author:zeke
    
    pass System Test!
    GET AC!!
*/
#include <iostream>
#include <queue>
#include <vector>
#include <iostream>
#include <vector>
#include <string>
#include <cassert>
#include <algorithm>
#include <functional>
#include <cmath>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <map>
#include <iomanip>
#include <utility>
#include <stack>
using ll = long long;
using ld = long double;
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define rep3(var, min, max) for (ll(var) = (min); (var) < (max); ++(var))
#define repi3(var, min, max) for (ll(var) = (max)-1; (var) + 1 > (min); --(var))
#define Mp(a, b) make_pair((a), (b))
#define F first
#define S second
#define Icin(s) \
    ll(s);      \
    cin >> (s);
#define Scin(s) \
    ll(s);      \
    cin >> (s);
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;
}
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef vector<V> VV;
typedef vector<P> VP;
ll MOD = 1e9 + 7;
ll INF = 1e18;

ll n, m, k;
vector<vector<pair<ll, ll>>> vec;
V reg;
bool dfs(ll x, ll f)
{
    if(f+1==k)
        return true;
    bool h = false;
    rep(i,vec[x].size()){
       // cout<<x<<" "<<vec[x][i].S<<" "<<reg[f+1]<<endl;
        if(vec[x][i].S==reg[f+1]){
            if(dfs(vec[x][i].F,f+1)){
                h = true;
                break;
            }
        }
    }
    return h;
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> n >> m >> k;
    vec.resize(n+1);
    rep(i,m){
        ll s,t,c;
        cin >> s >> t >> c;
        vec[s].push_back({t, c});
        vec[t].push_back({s, c});
    }
    reg.resize(k);
    rep(i,k){
        cin >> reg[i];
    }
    V res;
    reverse(all(reg));
    rep(i,n+1){
        rep(j,vec[i].size()){
            if(vec[i][j].S==reg[0]){
               // cout<<i<<" "<<vec[i][j].S<<endl;
                if(dfs(vec[i][j].F,0)){
                 //   cout<<i<<endl;
                    res.push_back(i);
                //    break;
                }
            }
        }
    }
     decltype(res)::iterator result = std::unique(res.begin(), res.end());
      res.erase(result, res.end());
    //sort(all(res));
    //unique(all(res));
    cout<<res.size()<<endl;
    rep(i,res.size()){
        cout << res[i] << " ";
    }
    cout << endl;
}