#include "bits/stdc++.h"
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> veci;
typedef vector<string> vecs;
template<class T,class U> using Hash=unordered_map<T,U>;

#define REP(i, a, n) for(ll i = a; i < n; i++)
#define RREP(i, a, n) for(ll i = n-1; i >= 0; i--)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, n) RREP(i, 0, n)
#define MD 1000000007

template<class T> T read(){T a;cin >> a;return a;}
template<class T> T read(T& a){cin >> a;}
template<class T> void rarr(T a, int n){for(int i = 0; i < n; i++) {cin >> a[i];}}
template<class T> void write(T a){cout << a << endl;}
template<class T> void writes(vector<T> a, char* c = " "){cout << a[0];for(int i = 1; i < a.size(); i++)cout << c << a[i];cout << endl;;}
void write(double a){cout << fixed << setprecision(12) << a << endl;}
template<class T> void warr(T a, int n, char* c = " "){cout << a[0];for(int i = 1; i < n; i++)cout << c << a[i];cout << endl;}
ll gcd(ll a, ll b){while(true){ll k = a % b;if(k == 0)return b;a = b;b = k;}}
ll comb(ll n, ll m){ll p=1;m=min(m,n-m);for(ll i=1;i<=m;i++){p*=n-i+1;p/=i;}return p;}

int main(void)
{
    Hash<ll,vector<pair<int,int>>> h;
    ll n,m,k,d[1000];
    cin>>n>>m>>k;
    rep(i,m){
        int a,b,c;
        cin>>a>>b>>c;
        if(h.count(c)==0)
            h[c]=vector<pair<int,int>>();
        h[c].push_back(pair<int,int>(a,b));
        h[c].push_back(pair<int,int>(b,a));
    }
    rarr(d,k);
    bool res[101]={0};
    rep(j,h[d[0]].size())
        res[h[d[0]][j].second]=true;
    REP(i,1,k){
        bool t[101]={0};
        auto& v=h[d[i]];
        rep(j,v.size()){
            if(res[v[j].first])
                t[v[j].second]=true;
        }
        REP(i,1,n+1)
            res[i]=t[i];
    }
    int sum=0;
    veci v;
    REP(i,1,n+1)
        if(res[i]){sum++;v.push_back(i);}
    write(sum);
    warr(v,v.size());
	return 0;
}