#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 205

vector<P> G[MAX_N];

int main() {
    int n, m, k;
    cin >> n >> m >> k;
    int f[n+1] = {};
    srep(i,1,n+1)f[i] = 1;
    rep(i,m){
        int a,b,c;
        cin >> a >> b >> c;
        G[a].push_back(P(b,c));
        G[b].push_back(P(a,c));
    }
    rep(loop,k){
        int d;
        cin >> d;
        int g[n+1] = {};
        srep(i,1,n+1){
            if(f[i] == 0)continue;
            rep(j,G[i].size()){
                if(G[i][j].second == d){
                    g[G[i][j].first] = 1;
                }
            }
        }
        rep(i,n+1)f[i] = g[i];
    }
    int cnt =0;
    rep(i,n+1)cnt += f[i];
    cout << cnt << endl;
    rep(i,n+1)if(f[i])cout << i << ' ';
    cout << endl;
    return 0;
}