# -*- coding: utf-8 -*-

from collections import deque

N,M,K = map(int, input().split())
a = [-1]
b = [-1]
c = [-1]
for i in range(M):
    s,t,u = map(int, input().split())
    a.append(s)
    b.append(t)
    c.append(u)
d = list(map(int, input().split()))

answer = []

# スタート町のセット
start_towns = deque()
end_towns = deque()
for i in range(1, M+1):
    if d[0]==c[i]:
        start_towns.append(a[i])
        start_towns.append(b[i])
# スタート町を起点に1ステップずつ幅優先探索
for i in range(1, K):
    es_cost = d[i]
    while len(start_towns) > 0:
        town = start_towns.popleft()
        for j in range(1,M+1):
            if c[j]==es_cost and town == a[j]:
                end_towns.append(b[j])
            elif c[j]==es_cost and town == b[j]:
                end_towns.append(a[j])
    if i < K-1:
        start_towns = end_towns
        end_towns = deque()

# end_townsが答え
for t in end_towns:
    answer.append(t)
answer.sort()
print(len(answer))
answer_str = str(answer[0])
for i in range(1, len(answer)):
    answer_str += ' ' + str(answer[i])
print(answer_str)