#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; };


int p[1010][110];
int a[1010], b[1010], c[1010], d[1010];

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

	rep(i,0,m) {
		cin >> a[i] >> b[i] >> c[i];
	}
	rep(i, 0, k)cin >> d[i];

	rep(i, 1, n+1)p[0][i] = 1;

	rep(i, 1, k+1)rep(j,0,m) {
		if (d[i-1] == c[j]) {
			if (p[i - 1][a[j]])p[i][b[j]] = 1;
			if (p[i - 1][b[j]])p[i][a[j]] = 1;
		}
	}
	int ans = 0;
	rep(i, 1, n+1)ans += p[k][i];
	cout << ans << endl;

	rep(i, 1, n+1) {
		if (p[k][i]) {
			cout << i << " ";
		}
	}
	cout << endl;
	return 0;
}