# -*- coding: utf-8 -*-
"""
No.92 逃走経路
https://yukicoder.me/problems/no/92

"""
import sys
from sys import stdin
input = stdin.readline


def solve(N, cities, logs):
    possibilities = set([x for x in range(1, N+1)])

    for l in logs:
        np = set()
        for p in possibilities:
            for dest, cost in cities[p]:
                if cost == l:
                    np.add(dest)
        possibilities = np

    ans = list(possibilities)
    ans.sort()
    return ans


def main(args):
    N, M, K = map(int, input().split())
    cities = [[] for _ in range(N+1)]
    for _ in range(M):
        a, b , c = map(int, input().split())
        cities[a].append([b, c])
        cities[b].append([a, c])
    logs = [int(x) for x in input().split()]

    ans = solve(N, cities, logs)
    print(len(ans))
    print(*ans)


if __name__ == '__main__':
    main(sys.argv[1:])