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


bool now[2000];
bool nex[2000];

int main(){
    int N, M, K;
    cin >> N >> M >> K;
    vector<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]--;
    }
    vector<int> d(K);
    for (int i = 0; i < K; i++)
    {
        cin >> d[i];
    }
    for (int i = 0; i < N; i++)
    {
        now[i] = true;
        nex[i] = false;
    }

    for (int i = 0; i < K; i++)
    {
        for (int j = 0; j < M; j++)
        {
            if (c[j] != d[i]) continue;
            nex[a[j]] |= now[b[j]];
            nex[b[j]] |= now[a[j]];
        }
        for (int j = 0; j < N; j++)
        {
            now[j] = nex[j];
            nex[j] = false;
        }
    }

    int count = 0;
    for (int i = 0; i < N; i++)
    {
        if (now[i]){
            count++;
        }
    }
    cout << count << endl;

    for (int i = 0; i < N; i++)
    {
        if (now[i]){
            if (--count) cout << (i + 1) << " "; 
            else cout << (i + 1) << endl;
        }
    }
}