n,m,k=map(int,input().split())
g=[[] for _ in range(n+1)]
for _ in range(m):
    a,b,c=map(int,input().split())
    g[a].append([b,c])
    g[b].append([a,c])
d=list(map(int,input().split()))
kouho=set(range(1,n+1))
for i in range(k):
    tmp=set()
    for j in kouho:
        for v,c in g[j]:
            if c==d[i]:
                tmp.add(v)
    kouho=tmp
print(len(kouho))
kouho=list(kouho)
kouho.sort()
print(*kouho)