from collections import *
from itertools import *
from heapq import *
from functools import *
import sys,math
input = sys.stdin.readline

N,M,K = map(int,input().split())
e = [[] for _ in range(N)]
for _ in range(M):
    a,b,c = map(int,input().split())
    a -= 1
    b -= 1
    e[a].append((b,c))
    e[b].append((a,c))
D = list(map(int,input().split()))

cnt = [[False]*(K+1) for _ in range(N)]
for i in range(N):
    cnt[i][0]=True

for i in range(K):
    
    d = D[i]
    
    for j in range(N):
        
        if cnt[j][i]:
            
            for ix,ic in e[j]:
                
                if ic==d:
                    
                    cnt[ix][i+1] = True
                    
ans = []
for i in range(N):
    if cnt[i][-1]:
        ans.append(i+1)
print(len(ans))
print(*ans)