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

fn main() {
    let mut nmk = String::new();
    std::io::stdin().read_line(&mut nmk).ok();
    let nmk: Vec<usize> = nmk.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nmk[0];
    let m = nmk[1];
    let mut t2c2t: Vec<HashMap<usize, Vec<usize>>> = vec![HashMap::new(); n];
    let mut c2ts: HashMap<usize, Vec<usize>> = HashMap::new();
    for _ in 0..m {
        let mut abc = String::new();
        std::io::stdin().read_line(&mut abc).ok();
        let abc: Vec<usize> = abc.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
        let a = abc[0] - 1;
        let b = abc[1] - 1;
        let c = abc[2];
        if let Some(x) = t2c2t[a].get_mut(&c) {
            (*x).push(b);
        } else {
            t2c2t[a].insert(c, vec!{b});
        }
        if let Some(x) = t2c2t[b].get_mut(&c) {
            (*x).push(a);
        } else {
            t2c2t[b].insert(c, vec!{a});
        }
        if c2ts.get(&c).is_none() {
            c2ts.insert(c, vec!{a, b});
        } else {
            if !c2ts.get(&c).unwrap().contains(&a) {
                c2ts.get_mut(&c).unwrap().push(a);
            }
            if !c2ts.get(&c).unwrap().contains(&b) {
                c2ts.get_mut(&c).unwrap().push(b);
            }
        }
    }
    let mut d = String::new();
    std::io::stdin().read_line(&mut d).ok();
    let mut d: VecDeque<usize> = d.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let mut cands: VecDeque<usize> = VecDeque::new();
    let l = d.pop_front().unwrap();
    c2ts.get(&l).unwrap().iter().for_each(|t| cands.push_back(*t));
    while !d.is_empty() {
        let cost = d.pop_front().unwrap();
        let lim = cands.len();
        for _ in 0..lim {
            let town = cands.pop_front().unwrap();
            if let Some(x) = t2c2t[town].get(&cost) {
                (*x).iter().for_each(|t| {
                    cands.push_back(*t);
                });
            }
        }
        let mut temp: Vec<usize> = cands.iter().map(|i| *i).collect();
        temp.sort();
        temp.dedup();
        cands = temp.iter().map(|i| *i).collect();
    }
    println!("{}", cands.len());
    println!("{}", cands.iter().map(|i| (i+1).to_string()).collect::<Vec<String>>().join(" "));
}