import sys


def input(): return sys.stdin.readline().rstrip()


def main():
    N, M, K = map(int, input().split())
    abc = [list(map(int, input().split())) for i in range(M)]
    *d, = map(int, input().split())

    adj = [[] for i in range(N+1)]
    for a, b, c in abc:
        adj[a].append((b, c))
        adj[b].append((a, c))

    *cur, = range(1, N+1)
    for e in d:
        ncur = []
        for v in cur:
            for u, c in adj[v]:
                if c == e:
                    ncur.append(u)
        cur = list(set(ncur))

    print(len(cur))
    print(*cur)


if __name__ == '__main__':
    main()