#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define p(s) cout<<(s)<<endl
#define REP(i,n,N) for(int i=n;i<N;i++)
#define RREP(i,n,N) for(int i=N-1;i>=n;i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define F first
#define S second
typedef long long int ll;
using namespace std;
const int inf=1e9+7;

int N, M, K;
vector<pair<int, int>> edge[110];
set<int> s;
int main(){
    cin>>N>>M>>K;
    REP(i,0,M){
        int a,b,c;
        cin>>a>>b>>c;
        a--;
        b--;
        edge[a].push_back({b,c});
        edge[b].push_back({a,c});
    }
    REP(i,0,N){
        s.insert(i);
    }
    REP(i,0,K){
        int d;
        cin>>d;
        set<int> nexts;
        for(auto st:s){
            for(auto v:edge[st])
            if(d==v.second){
                nexts.insert(v.first);
            }
        }
        s = nexts;
    }
    p(s.size());

    for(auto st:s){
        cout<<st+1<<" ";
    }
    cout<<endl;
    return 0;
}