#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

struct edge {int from, to, cost;};

int d[1005], dp[1005][105];

int main(){
    int n, m, k, cnt = 0; cin>>n>>m>>k;
    vector<edge> E(m);
    for(int i=0;i<m;i++) cin>>E[i].from>>E[i].to>>E[i].cost;
    for(int i=0;i<k;i++) cin>>d[i];

    for(int i=1;i<=n;i++) dp[0][i] = 1;
    for(int i=1;i<=k;i++){
        for(auto it:E){
            if(it.cost==d[i-1]&&dp[i-1][it.from]) dp[i][it.to] = 1;
            if(it.cost==d[i-1]&&dp[i-1][it.to]) dp[i][it.from] = 1;
        }
    }

    vector<int> ans;
    for(int i=1;i<=n;i++){
        if(dp[k][i]){
            cnt++;
            ans.push_back(i);
        }
    }

    cout<<cnt<<endl;
    for(int it:ans) cout<<it<<' ';
    cout<<endl;
    return 0;
}