import sequtils,strutils

type
    road = tuple[to, cost : int]
var
    N,M,K,a,b,c : int
    D : seq[int]
    
(N, M, K) = stdin.readline.split.map(parseInt)
var
    town = newSeqWith(N + 1,newSeq[road](0))
    P : set[int8]
for m in 1..M:
    (a,b,c) =stdin.readline.split.map(parseInt)
    town[a].add((b,c))
    town[b].add((a,c))
    
D = stdin.readline.split.map(parseInt)
for n in 1..N:
    P.incl(n.int8)
for d in D:
    var s : set[int8]
    for p in P:
        for r in town[p.int]:
            if r.cost == d:
                s.incl(r.to.int8)
    P = s
echo P.card
var ans = newSeq[int](0)
for i in P:
    ans.add(i)
echo ans.join(" ")