n,m,k=map(int,input().split())
l=[[]for _ in range(n+1)]
for _ in range(m):
    a,b,c=map(int,input().split())
    l[a].append([b,c])
    l[b].append([a,c])
d=list(map(int,input().split()))
dp=[[0]*(n+1)for _ in range(k+1)]
dp[0]=[1]*(n+1)
for i in range(k):
    for j in range(1,n+1):
        if not dp[i][j]:continue
        for t in l[j]:
            if t[1]==d[i]:
                dp[i+1][t[0]]=1
print(sum(dp[k]))
print(*[i for i in range(n+1)if dp[k][i]])