import sys
import numpy as np
input=lambda:sys.stdin.readline().rstrip()
N,M,K=map(int,input().split())
mat={}
for i in range(M):
	a,b,c=map(int,input().split())
	if not c in mat:
		mat[c]=np.zeros((N,N))
	mat[c][a-1][b-1]=1
	mat[c][b-1][a-1]=1
D=list(map(int,input().split()))
pot=np.ones((N,1))
for i in D:
	pot=mat[i]@pot
	for i in range(N):
		pot[i][0]=min(1,pot[i][0])
ans=[]
for i in range(N):
	if pot[i][0]:
		ans.append(i+1)
print(len(ans))
print(*ans)