#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <set>
using namespace std;

#define RREP(i,s,e) for (i = e-1; i >= s; i--)
#define rrep(i,n) RREP(i,0,n)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 1e8

typedef long long ll;

int main() {
    int i, n, m, k;
    ll d[1000];
    set<int> s[2];
    vector<map<int,vector<int>>> edges;
    cin >> n >> m >> k;
    edges.resize(n+1);
    rep (i,m) {
        int a, b, c;
        cin >> a >> b >> c;
        edges[a][c].push_back(b);
        edges[b][c].push_back(a);
    }
    rep (i,k) cin >> d[i];
    rep (i,n) s[0].insert(i+1);
    rep (i,k) {
        for (int a : s[i%2]) {
            for (int b : edges[a][d[i]])
                s[(i+1)%2].insert(b);
        }
        s[i%2].clear();
    }
    cout << s[k%2].size() << endl;
    for (int a : s[k%2])
        cout << a << " ";
    cout << endl;
    return 0;
}