use std::collections::{BTreeSet, HashMap};

fn main() {
    let mut xx = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut xx).ok();
    let xx: Vec<usize> = xx.split_whitespace().flat_map(str::parse).collect();

    let n = xx[0];
    let m = xx[1];

    let mut e = vec![HashMap::<usize, Vec<_>>::new(); n + 1];
    for x in xx[3..3 * (m + 1)].chunks(3) {
        e[x[0]].entry(x[2]).or_default().push(x[1]);
        e[x[1]].entry(x[2]).or_default().push(x[0]);
    }

    let mut pp: BTreeSet<usize> = (1..=n).collect();
    for &k in &xx[3 * (m + 1)..] {
        let mut new_pp = BTreeSet::new();
        for &p in &pp {
            if let Some(v) = e[p].get(&k) {
                new_pp.extend(v);
            }
        }
        pp = new_pp;
    }

    let output = pp.iter().map(|&p| p.to_string()).collect::<Vec<String>>();

    println!("{}", pp.len());
    println!("{}", output.join(" "));
}