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

int solve(int n, pair<int, int> &hfs);

int main() {
	int n, m, k;
	cin >> n >> m >> k;

	vector<pair<long, pair<int, int> > > h;
    h.resize(m);
	multiset<long> c1;
    int a,b;
    long c;
	for (int i = 0; i<m; i++) {
		cin >> a >> b >> c;
        c1.insert(c);
		h[i] = make_pair(c,make_pair(a,b));
	}

	long x;
	set<int> nr;
	for (int i = 0; i < k; i++) {
        set<int> r;
		cin >> x;
        auto itc1 = c1.find(x);
        int f = distance(c1.begin(),itc1);
		int s = nr.size();
		while (1) {
            if(*(itc1)==x){
			if (i == 0) {
				r.insert(h[f].second.first);
				r.insert(h[f].second.second);
			}
			else {
				int y;
                auto itnr = nr.begin();
				for (int j = 0; j <s; j++) {
					y = solve(*(itnr), h[f].second);
					if (y) {
						r.insert(y);
					}
                    itnr++;
				}
			}
			itc1++; 
            f++;
            }else break;
		}
        nr.clear();
        nr=r;
	}
    auto itnr = nr.begin(); 
	cout << nr.size() << endl;
	for (int i=0;i<nr.size(); i++) {
		if (i) cout << " ";
		cout << *(itnr);
        itnr++;
	}
	cout << endl;

	return 0;
}

int solve(int n, pair<int, int> &hfs) {
	if (n == hfs.first) {
		return hfs.second;
	}
	else if (n == hfs.second) {
		return hfs.first;
	}
	return 0;
}