#include<stdio.h>

int N,M,K;

int p[1001][100]={0};
int F[100][100][1000] = {0};
int fsz[100][100] = {0};
int D[1000] = {0};




void nyrn(int index,int n){
    int i,j,k;
    if (index == K+1)return;
    if (p[index][n])return;
    p[index][n] = 1;
        for (j=0;j<N;j++){
            for (k=0;k<fsz[n][j];k++){
                if (F[n][j][k] == D[index]){
                    nyrn(index+1,j);
                }
            }
        }
}

int main(void){
    scanf("%d %d %d",&N,&M,&K);
    int i=0;
    for (i=0;i<M;i++){
        int a,b,c;scanf("%d %d %d",&a,&b,&c);
        a--;
        b--;
        F[a][b][fsz[a][b]] = c;
        F[b][a][fsz[b][a]] = c;
        fsz[a][b]++;
        fsz[b][a]++;
    }
    for (i=0;i<K;i++)scanf("%d",&D[i]);

    for (i=0;i<N;i++)nyrn(0,i);
    int anss=0,ans[100]={0};
    for (i=0;i<N;i++){
        if (p[K][i]){
            ans[anss] = i;
            anss++;
        }
    }
    printf("%d\n",anss);
    for (i=0;i<anss;i++){
        printf("%d",ans[i]+1);
        if (i!=anss-1)printf(" ");
    }
    printf("\n");
    return 0;
}