import kotlin.math.PI


fun main(arr:Array<String>) {
    val(cityCount, roadCount, logCount) = readLine()!!.split(" ").map { it.toInt() }
    val roads = mutableMapOf<Int,MutableMap<Int, MutableMap<Long, Boolean>>>()
    (0 until roadCount).forEach {
        val(city1, city2, cost) = readLine()!!.split(" ").map { it.toInt() }
        if(!roads.containsKey(city1)) {
            roads[city1] = mutableMapOf()
        }
        if(!roads.containsKey(city2)) {
            roads[city2] = mutableMapOf()
        }
        if(!roads[city1]!!.containsKey(city2)) {
            roads[city1]!![city2] = mutableMapOf()
        }
        if(!roads[city2]!!.containsKey(city1)) {
            roads[city2]!![city1] = mutableMapOf()
        }

        roads[city1]!![city2]!![cost.toLong()] = true
        roads[city2]!![city1]!![cost.toLong()] = true
    }

    val log = readLine()!!.split(" ").map { it.toLong() }
    val ans = Proc(roads, log).getAns()
    println(ans.size)
    println(ans.joinToString(" "))
}

class Proc(val roads:Map<Int, Map<Int,Map<Long, Boolean>>>, val log:List<Long>) {
    public fun getAns():List<Int> {


        var currentList = roads.map { a->a.value.filter { b-> log[0] in b.value.keys }.map { it.key }.toMutableList() }.reduce { acc, list -> acc.union(list).toMutableList() }.toList()
        for(i in log.drop(1)) {
            currentList = currentList.map { a->roads[a]?.let { b-> b.filter { i in it.value.keys }.keys.toMutableList() }?: mutableListOf() }.reduce { acc, mutableList -> acc.union(mutableList).toMutableList() }.toList()
        }
        return currentList
    }
}