n, m ,k = list(map(int, input().split(' ')))
abcm = [None] * m
for i in range(m):
    abcm[i] = list(map(int, input().split(' ')))

dk = list(map(int, input().split(' ')))


def solver(cp, x):
    if x == k:
        return [cp]

    result = []
    for i in range(m):
        bg = abcm[i]

        if bg[0] == cp and bg[2] == dk[x]:
            r = solver(bg[1], x + 1)
            if len(r) != 0:
                result.extend(r)
        elif bg[1] == cp and bg[2] == dk[x]:
            r = solver(bg[0],  x + 1)
            if len(r) != 0:
                result.extend(r)
    return result

c = 0
cps = set()
for i in range(1, n + 1):
    result = solver(i, 0)
    c += len(result)
    for j in result:
        cps.add(j)
        
cps = sorted(cps)
print(c)
for i in range(c):
    print(cps[i] ,end=' ')
print()