#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <climits>
#include <typeinfo>
#include <utility> 
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(int i = m;i < n;++i)
#define pb push_back
#define fore(i,a) for(auto &i:a)
#define rrep(i,m,n) for(int i = m;i >= n;--i)
#define INF INT_MAX/2
using namespace std;
using ll = long long;
using R = double;
const ll MOD = 1e9 + 7;
const ll inf = 1LL << 50;
struct edge { ll from; ll to; ll cost; };


ll n, m, k;
vector<vector<ll>>e[1010];
vector<ll>d;

int dfs(int now,int num) {
	if (num == k)return 1;

	ll next = d[num];
	fore(x,e[next]) {
		if (x[1] == now) {
			if (dfs(x[0], num + 1))return 1;
		}
	}
	return 0;
}

int main(){
	cin >> n >> m >> k;

	rep(i, 0, m) {
		ll a, b, c;
		cin >> a >> b >> c; 

		e[c].pb({a,b});
		e[c].pb({b,a});
	}

	rep(i, 0, k) {
		ll D;
		cin >> D;
		d.pb(D);
	}
	reverse(all(d));

	ll ans = 0;
	vector<ll>town;
	fore(x,e[d[0]]) {
		if (dfs(x[0], 1)) {
			ans++;
			town.pb(x[1]);
		}
	}
	cout << ans << endl;
	sort(all(town));
	rep(i, 0, ans) {
		if (i)cout << " ";
		cout << town[i];
	}
	cout << endl;

	return 0;
}