#include <iostream>
#include <vector>
#include <unordered_map>
#include <map>
typedef long long int64;
using namespace std;
unordered_map<int64, unordered_map<int64, unordered_map<int64, bool>>> m3;
vector<int> d;
map<int, bool> res;
int n, m, k;
void solve(int cur, int deep) {
    if(deep >= k) {
        res[cur] = true;
        return;
    }
    if(m3.count(cur) == 0)
        return;
    for(auto m2 : m3[cur]) {
        if(m2.second.count(d[deep]) != 0) {
            solve(m2.first, deep + 1);
        }
    }
}

int main(void)
{
    cin >> n >> m >> k;
    for(int i = 0; i < m; i++) {
        int64 a, b, c;
        cin >> a >> b >> c;
        m3[a][b][c] = true;
        m3[b][a][c] = true;
    }
    d.resize(k);
    for(int i = 0; i < k; i++) {
        cin >> d[i];
    }
    for(int i = 0; i < n; i++) {
        solve(i + 1, 0);
    }
    bool f = true;
    cout << res.size() << endl;
    for(auto r : res) {
        if(f)
            f = false;
        else
            cout << " ";
        cout << r.first;
    }
    cout << endl;
    return 0;
}