#include<map>
#include<set>
#include<cstdio>
#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cstring>
using namespace std;

typedef long long LL;
typedef vector<int> VI;

#define REP(i,n) for(int i=0; i<int(n); i++)
#define EACH(i,c) for(__typeof((c).begin()) i=(c).begin();i!=(c).end();i++)

template<class T> inline T &amin(T &a, T b) { if (a>b) a=b; return a; }
template<class T> inline T &amax(T &a, T b) { if (a<b) a=b; return a; }

int N, M, K;
map<int, vector<pair<int, int> > > mp; // cost -> [(v, v)]
int main() {
    scanf("%d%d%d", &N, &M, &K);
    REP (i, M) {
	int a, b, c;
	scanf("%d%d%d", &a, &b, &c);
	mp[c].push_back(make_pair(a, b));
    }

    int D;

    set<int> se;
    REP (i, N) se.insert(i+1);
    REP (i, K) {
    
	scanf("%d", &D);
	set<int> nxt;
	REP (i, mp[D].size()) {
	    int v = mp[D][i].first, w = mp[D][i].second;
	    if (se.count(w)) nxt.insert(v);
	    if (se.count(v)) nxt.insert(w);
	}
	se.swap(nxt);
    }

    printf("%d\n", (int)se.size());
    bool sp = false;
    EACH (it, se) {
	if (sp) putchar(' ');
	sp = true;
	printf("%d", *it);
    }
    putchar('\n');
    
    return 0;
}