#!/usr/bin/env python3

import array
import collections


Edge = collections.namedtuple("Edge", "source dest")


def possible_current_vertices(n, cost_to_edges, ds):
    possible_vertices = []
    possible_vertices.append(set(range(1, n + 1)))
    for index, d in enumerate(ds, start=1):
        vertices = {edge.dest for edge in cost_to_edges[
            d] if edge.source in possible_vertices[index - 1]}
        possible_vertices.append(vertices)
    return possible_vertices[-1]


def main():
    n, m, k = map(int, input().split())
    cost_to_edges = collections.defaultdict(set)
    for _ in range(m):
        a, b, c = map(int, input().split())
        cost_to_edges[c].add(Edge(a, b))
        cost_to_edges[c].add(Edge(b, a))
    ds = array.array("L", map(int, input().split()))
    answer = possible_current_vertices(n, cost_to_edges, ds)
    print(len(answer))
    print(" ".join(map(str, sorted(answer))))


if __name__ == '__main__':
    main()