N,M,K = [int(i) for i in input().split()]
a = [0]*M
b = [0]*M
c = [0]*M

for i in range(M):
    a[i],b[i],c[i] = map(int, input().split())

candidates = set(range(1,N+1))
for k in map(int, input().split()):
    new_candidates = set([])
    for i in range(M):
        if c[i] == k:
            if a[i] in candidates:
                new_candidates.add(b[i])
            if b[i] in candidates:
                new_candidates.add(a[i])
    candidates = new_candidates


print(len(candidates))
print(" ".join([str(i) for i in candidates]))