from collections import defaultdict
def solve():
    n, m, k = map(int, input().split())
    mip = defaultdict(list)
    mpi = defaultdict(list)
    for i in range(m):
        a, b, c = map(int, input().split())
        mpi[c, a].append(b)
        mpi[c, b].append(a)
        mip[c].append((a, b))
    d = tuple(map(int, input().split()))
    v = (set(), set())
    for a in mip[d[0]]:
        v[0].add(a[0])
        v[0].add(a[1])
    if k == 1:
        return v[0]
    a1 = 0
    a2 = 1
    for i in range(1, k):
        for x in v[a1]:
            for b in mpi[d[i], x]:
                v[a2].add(b)
        v[a1].clear()
        a1, a2 = a2, a1
    return v[a1]
v = sorted(solve())
print(len(v))
print(*v)