#include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<vector>
#include<set>
#include<list>
#include<queue>
#include<math.h>
#include<bitset>
using ll = long long;
using namespace std;

int main(){
    int n , m, k;
    cin >> n >> m >> k;
    vector<vector<int>> list(m, vector<int>(3));
    vector<int> fee(k), list1(m);
    set<int> now, can;
    for (int i = 0; i < m; i++){
        cin >> list[i][1] >> list[i][2] >> list[i][0];
    }
    for (int i = 0; i < k; i++){
        cin >> fee[i];
        if (i == 0) {
            for (int j = 0; j < m; j++){
                if (fee[0] == list[j][0]){
                    can.insert(list[j][1]);
                    can.insert(list[j][2]);
                }
            }
        }
    }
    sort(list.begin(), list.end());
    for (int i = 0; i < m; i++) list1[i] = list[i][0]; 
    for (int i = 1; i < k; i++){
        int idx = -1;
        auto itr = lower_bound(list1.begin(), list1.end(), fee[i]);
        if (itr != list1.end()) idx = distance(list1.begin(), itr);
        for (int j = idx; j < m; j++){
            if (list1[j] == fee[i]){
                if (can.find(list[j][1]) != can.end()) now.insert(list[j][2]);
                if (can.find(list[j][2]) != can.end()) now.insert(list[j][1]);
            } else break;
        }
        can = now;
    }
    cout << can.size() << endl;
    string delim = "";
    for (auto x : can){
        cout << delim << x;
        delim = " ";
    }
    cout << endl;
}