package main

import (
	"fmt"
	"strconv"
	"strings"
)

func main() {
	var n, m, k int
	fmt.Scan(&n, &m, &k)
	a := make([]int, m)
	b := make([]int, m)
	c := make([]int, m)
	for i, _ := range a {
		fmt.Scan(&a[i], &b[i], &c[i])
		a[i]--
		b[i]--
	}
	ans := make([]bool, n)
	for i, _ := range ans {
		ans[i] = true
	}
	for i := 0; i < k; i++ {
		var d int
		fmt.Scan(&d)
		next := make([]bool, n)
		for j, _ := range a {
			if c[j] != d {
				continue
			}
			if ans[a[j]] {
				next[b[j]] = true
			}
			if ans[b[j]] {
				next[a[j]] = true
			}
		}
		copy(ans, next)
	}
	res := make([]string, 0)
	for i, v := range ans {
		if v {
			res = append(res, strconv.Itoa(i+1))
		}
	}
	fmt.Println(len(res))
	fmt.Println(strings.Join(res, " "))
}