#include <bits/stdc++.h>
#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);
    vector<int> can(n);
    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[list[j][1]]++;
                    can[list[j][2]]++;
                }
            }
        }
    }

    sort(list.begin(), list.end(), [](const vector<int> &alpha,const vector<int> &beta){return alpha[0] < beta[0];});
    for (int i = 0; i < m; i++) list1[i] = list[i][0]; 
    for (int i = 1; i < k; i++){
        int idx = -1;
        vector<int> now(n);
        for (int r = 0; r < n; r++) {
            if (can[r]) {
                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[list[j][1]]) now[list[j][2]] = 1;
                        if (can[list[j][2]]) now[list[j][1]] = 1;
                    } else break;
                }
            }
        }
        swap(can, now);
    }
    cout << accumulate(can.begin(), can.end(), 0) << endl;
    string delim = "";
    for (int i = 0; i < n; i++){
        if (can[i]){
            cout << delim << i;
            delim = " ";
        }
    }
    cout << endl;
}