#include <iostream>
#include <cstring>
using namespace std;

bool pos[2][111];
int a[1111], b[1111], c[1111];

int main(){
    int N, M, K;
    cin >> N >> M >> K;
    
    for(int i=0;i<M;i++){
        cin >> a[i] >> b[i] >> c[i];
        
        --a[i];
        --b[i];
    }
    
    int curr = 0, next = 1;
    memset(pos[curr], true, sizeof(pos[curr]));
    
    for(int i=0;i<K;i++){
        int d;
        cin >> d;
        
        memset(pos[next], false, sizeof(pos[next]));
        for(int j=0;j<M;j++)if(c[j] == d){
            pos[next][a[j]] |= pos[curr][b[j]];
            pos[next][b[j]] |= pos[curr][a[j]];
        }
        
        swap(curr, next);
    }
    
    int cnt = 0;
    for(int i=0;i<N;i++)cnt += pos[curr][i];
    
    cout << cnt << endl;
    for(int i=0;i<N;i++)if(pos[curr][i])cout << (i + 1) << " ";
    
    
    return 0;
}