#region Header
#!/usr/bin/env python3
# from typing import *

import sys
import io
import math
import collections
import decimal
import itertools
from queue import PriorityQueue
import bisect
import heapq

def input():
    return sys.stdin.readline()[:-1]

sys.setrecursionlimit(1000000)
#endregion

# _INPUT = """# paste here...
# """
# sys.stdin = io.StringIO(_INPUT)



def main():
    N, M, K = map(int, input().split())
    G = [list() for _ in range(N)]
    d = dict()
    for _ in range(M):
        a, b, c = map(int, input().split())
        a -= 1
        b -= 1
        G[a].append((b, c))
        G[b].append((a, c))
        if c not in d:
            d[c] = set()
        d[c].add(a)
        d[c].add(b)
    D = list(map(int, input().split()))

    cities = d[D[0]]
    for i in range(1, K):
        if not cities:
            break
        cities1 = set()
        for a in cities:
            for (b, c) in G[a]:
                if c == D[i]:
                    cities1.add(b)
        cities = cities1
    print(len(cities))
    print(*sorted([a+1 for a in cities]))

if __name__ == '__main__':
    main()