#pragma GCC optimize("Ofast")
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
#include <deque>
#include <stack>
#include <sstream>
#include <utility>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <tuple>
#include <array>
#include <bitset>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline double time() {
    return static_cast<long double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,m,k; cin >> n >> m >> k;
    vector<vector<pair<int,int>>> g(n);
    for(int i=0;i<m;i++){
        int x,y,c; cin >> x >> y >> c;
        x--; y--;
        g[x].push_back({y,c});
        g[y].push_back({x,c});
    }
    vector<int> v;
    for(int i=0;i<n;i++){
        v.push_back(i);
    }
    while(k--){
        int d; cin >> d;
        vector<int> nv;
        for(int i:v){
            for(auto t:g[i]){
                if(t.second == d)nv.push_back(t.first);
            }
        }
        sort(nv.begin(), nv.end());
        nv.erase(unique(nv.begin(), nv.end()),nv.end());
        swap(v,nv);
    }
    cout << v.size() << "\n";
    for(int i=0;i<v.size();i++){
        if(i) cout << " ";
        cout << v[i]+1;
    }
    cout << "\n";
}