import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

N,M,K = map(int,readline().split())
ABC = tuple(tuple(map(int,readline().split())) for _ in range(M))
D = tuple(map(int,read().split()))

p = [True] * (N+1)
for d in D:
    q = [False] * (N+1)
    for a,b,c in ABC:
        if c != d:
            continue
        if p[a]:
            q[b] = True
        if p[b]:
            q[a] = True
    p = q

answer = [i for i,x in enumerate(p) if x]
print(len(answer))
print(*answer)