#include <iostream>
#include <vector>
#include <set>
#include <map>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
using namespace std;
int main() {
    // input
    int n, m, k; cin >> n >> m >> k;
    vector<map<int,vector<int> > > g(n);
    repeat (i,m) {
        int a, b, c; cin >> a >> b >> c; -- a; -- b;
        g[a][c].push_back(b);
        g[b][c].push_back(a);
    }
    vector<int> ds(k); repeat (i,k) cin >> ds[i];
    // search
    set<int> xs; repeat (i,n) xs.insert(i);
    for (int d : ds) {
        set<int> ys;
        for (int x : xs) {
            if (g[x].count(d)) for (int y : g[x][d]) {
                ys.insert(y);
            }
        }
        xs = ys;
    }
    // output
    cout << xs.size() << endl;
    for (int x : xs) cout << x + 1 << ' ';
    cout << endl;
    return 0;
}