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

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

        if bg[0] == cp and bg[2] == dk[x]:
            r = solver(bg[1], x + 1)
            return r
            
        if bg[1] == cp and bg[2] == dk[x]:
            r = solver(bg[0],  x + 1)
            return r
 
    return None

c = 0
cps = set()
for i in range(1, n + 1):
    result = solver(i, 0)

    if result is not None:
        c += 1
        cps.add(result)
        
cps = sorted(cps)
print(c)
for i in range(c):
    print(cps[i] ,end=' ')
print()