#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>

#define REP(i,n) for(int (i)=0;(i)<(n);(i)++)
#define FOR(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define RREP(i,a) for(int (i)=(a)-1;(i)>=0;(i)--)
#define FORR(i,a,b) for(int (i)=(a)-1;(i)>=(b);(i)--)
#define PI acos(-1.0)
#define DEBUG(C) cout<<C<<endl;
#define VI vector<int>
#define VII vector<VI>
#define VL vector<LL>
#define VLL vector<VL>
#define VD vector<double>
#define VDD vector<VD>
#define PII pair<int,int>
#define PDD pair<double,double>
#define PLL pair<LL,LL>
#define VPII vector<PII>
#define ALL(a) (a).begin(),(a).end()
#define SORT(a) sort(ALL(a))
#define REVERSE(a) reverse(ALL(a))
#define MP make_pair
#define FORE(a,b) for(auto &&a:b)
#define FIND(s,n) s.find(n)!=s.end()

using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int INF=1e9;
const int MOD=INF+7;

int N,M,K;
vector<VPII> graph;
VL d;

int main (void) {
    cin >> N >> M >> K;
    graph = vector<VPII>(N);
    REP (i, M) {
        int a, b, c;
        cin >> a >> b >> c;
        a--;b--;
        graph[a].emplace_back(MP(b, c));
        graph[b].emplace_back(MP(a, c));
    }
    d = VL(K);
    REP (i, K) cin >> d[i];
    vector<bool> now(N, true),next(N, false);
    REP (i, K) {
        REP (j, N) {
            if (!now[j]) continue;
            FORE (el,graph[j]) {
                if (el.second == d[i]) next[el.first] = true;
            }
        }
        now = next;
        fill (ALL(next), false);
    }
    set<int> ans;
    REP (i, N) if(now[i]) ans.insert(i);
    cout << ans.size() << endl;
    FORE (el, ans) cout << el + 1 << " ";
    if (!ans.empty()) cout << endl;
}