#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
int INF = 1e9;
int MOD = 1e9+7;
int p[1010][110];
main(){
    int N,M,K,A[1000],B[1000],C[1000],D[1000];
    cin >> N >> M >> K;
    for(int i = 0;i < M;i++)cin >> A[i] >> B[i] >> C[i];
    for(int i = 0;i < K;i++)cin >> D[i];
    for(int i = 0;i < M;i++){
        if(D[0] == C[i]){
            p[0][A[i]] = 1;
            p[0][B[i]] = 1;
        }
    }
    for(int i = 1;i < K;i++){
        for(int j = 0;j < M;j++){
            if(D[i] == C[j]){
                if(p[i-1][A[j]])p[i][B[j]] = 1;
                if(p[i-1][B[j]])p[i][A[j]] = 1;
            }
        }
    }
    cout << accumulate(p[K-1],p[K-1]+101,0) << endl;
    for(int i = 1;i <= 100;i++)if(p[K-1][i])printf("%d ",i);
    cout << endl;
}