#include <iostream>
#include <vector>
#include <queue>
using namespace std;
using P = pair<int, int>;

int main(){
    int n, m, k; cin >> n >> m >> k;
    vector<vector<P>> G(n);
    for(int i = 0; i < m; i++){
        int a, b, c; cin >> a >> b >> c;
        a--; b--;
        G[a].emplace_back(b, c);
        G[b].emplace_back(a, c);
    }
    vector<int> d(k);
    for(auto &it: d) cin >> it;
    vector<vector<bool>> mem(k+1, vector<bool>(n, false));
    for(int i = 0; i < n; i++) mem[0][i] = true;
    for(int i = 0; i < k; i++){
        for(int j = 0; j < n; j++){
            if(!mem[i][j]) continue;
            for(auto &it: G[j]){
                if(it.second == d[i]) mem[i+1][it.first] = true;
            }
        }
    }
    
    vector<int> ans;
    for(int i = 0; i < n; i++){
        if(mem[k][i]) ans.emplace_back(i+1);
    }
    cout << ans.size() << '\n';
    for(int i = 0; i < ans.size(); i++){
        if(i != 0) cout << " ";
        cout << ans[i];
    }
    cout << '\n';
    return 0;
}