#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    int n,m,k;
    cin>>n>>m>>k;
    int a[m],b[m],c[m];
    for(int i=0;i<m;i++){
        cin>>a[i]>>b[i]>>c[i];
        a[i]--;
        b[i]--;
    }
    int d[k];
    for(int i=0;i<k;i++)cin>>d[i];
    bool poss[k][n] {};
    for(int i=0;i<n;i++)poss[0][i]=true;
    for(int i=1;i<=k;i++)
        for(int j=0;j<m;j++){
            if (d[i-1]!=c[j]) continue;
            poss[i][a[j]] |= poss[i-1][b[j]];
            poss[i][b[j]] |= poss[i-1][a[j]];
        }
    int cnt=0;
    for (int i=0;i<n;i++) if (poss[k][i]) cnt++;
    cout<<cnt<<endl;
    for (int i=0;i<n;i++) if (poss[k][i]) cout<<i+1<<' ';
    cout<<endl;
    return 0;
}