package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)
var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func main() {
	sc.Split(bufio.ScanWords)
	n, m, k := nextInt(), nextInt(), nextInt()
	loads, towns := make([][3]int, 0, 1000), make([]bool, n+1)
	for i := 0; i < m; i++ {
		a, b, c := nextInt(), nextInt(), nextInt()
		loads = append(loads, [3]int{a, b, c})
	}
	times := make([]int, k)
	for i := range times {
		times[i] = nextInt()
	}

	for _, v := range loads {
		if v[2] == times[0] {
			towns[v[0]] = true
			towns[v[1]] = true
		}
	}

	for _, c := range times[1:] {
		next := make([]bool, n+1)
		for _, v := range loads {
			if v[2] != c {
				continue
			}

			if towns[v[0]] {
				next[v[1]] = true
			}
			if towns[v[1]] {
				next[v[0]] = true
			}
		}

		towns = next
	}

	ans := make([]int, 0, 100)
	for i, v := range towns {
		if v {
			ans = append(ans, i)
		}
	}
	fmt.Println(len(ans))
	s := fmt.Sprint(ans)
	fmt.Println(s[1 : len(s)-1])
}

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	i, _ := strconv.Atoi(nextLine())
	return i
}