#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())

ll n, m, k;
vector<vector<pair<ll, ll>>> g;
vector<ll> d;
vector<vector<bool>> dp;

void dfs(ll v, ll depth = 0) {
    if (dp[v][depth]) return;
    dp[v][depth] = true;
    if (depth == (k - 1)) return;
    for(auto x : g[v]) {
        ll u = x.first, c = x.second;
        if (d[depth + 1] == c) {
            dfs(u, depth + 1);
        }
    }
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    cin >> n >> m >> k;
    g.resize(n);
    rep(i, m) {
        ll a, b, c;
        cin >> a >> b >> c;
        a--; b--;
        g[a].push_back(make_pair(b, c));
        g[b].push_back(make_pair(a, c));
    }
    d.resize(k);
    rep(i, k) cin >> d[i];
    dp.resize(n, vector<bool>(k, false));
    rep(v, n) {
        for(auto x : g[v]) {
            ll u = x.first, c = x.second;
            if (c == d[0]) dfs(u);
        }
    }
    vector<ll> ans;
    rep(i, n) {
        if (dp[i][k - 1]) ans.push_back(i);
    }
    printf("%lld\n", sz(ans));
    rep(i, sz(ans)) printf("%lld%s", ans[i] + 1, (i == (sz(ans) - 1)) ? "\n" : " ");
    return 0;
}