# -*- coding:utf-8 -*-
from collections import defaultdict

if __name__ == "__main__":
	n,m,k = map(int,raw_input().split())
	roads = defaultdict(set)
	for i in xrange(m):
		a,b,c = map(int,raw_input().split())
		roads[c].add((a,b))
	D = map(int,raw_input().split())
	now = []
	prev = []
	for i in roads[D[0]]:
		now.append(i[0])
		now.append(i[1])
	for d in D[1::]:
		prev = now
		now = []
		for i in roads[d]:
			if i[0] in prev:
				now.append(i[1])
			if i[1] in prev:
				now.append(i[0])
	now.sort()
	now = map(str,now)
	print len(now)
	print ' '.join(now)