#include <math.h>
#include <string.h>
#include <stdio.h>

#define NMAX	(100)
#define TMAX	(1000)
#define INF		(99999999)

int toll[TMAX+5];

typedef struct{
	int lnum;
	int loadA[TMAX+5];
	int loadB[TMAX+5];
}TOWN;

TOWN town[NMAX+3];

int main(void){
	int nowTown[NMAX+5];
	
	int i,j,k, N, M, K;
	int cnt=0;
	int minTown = INF;
	
	scanf("%d %d %d", &N, &M, &K);
	for(i=0;i<M;i++){
		int a,b,c;
		int ltmp;
		scanf("%d %d %d", &a, &b, &c);
		
		ltmp = town[a].lnum;
		town[a].loadA[ltmp] = b;
		town[a].loadB[ltmp] = c;
		town[a].lnum += 1;
		
		ltmp = town[b].lnum;
		town[b].loadA[ltmp] = a;
		town[b].loadB[ltmp] = c;
		town[b].lnum += 1;
		
		
	}
	for(i=0;i<K;i++){
		scanf("%d", &toll[i]);
		toll[i+1] = 0;
	}
	
	for(i=0;i<=N;i++){ nowTown[i] = 1;}
	for(i=0;i<K;i++){
		int ntTmp[NMAX+5]={0};
		
		for(j=1;j<=N;j++){
			int ltmp = town[j].lnum;
			if(nowTown[j] != 1){continue;}
			
			for(k=0;k<ltmp;k++){
				if( town[j].loadB[k] == toll[i] ){
					ntTmp[ town[j].loadA[k] ] = 1;
				}
			}
		}
		
		for(j=0;j<=N;j++){nowTown[j] = ntTmp[j];}
	}
	
	
	
	
	for(i=1;i<=N;i++){
		if(nowTown[i] == 1){
			if(i < minTown){
				minTown = i;
			}
			
			cnt++;
		}
	}
	
	printf("%d\n", cnt);
	printf("%d", minTown);
	for(i=minTown+1;i<=N;i++){
		if(nowTown[i] == 1){
			printf(" %d", i);
		}
	}
	printf("\n");
	
	return 0;
}