import sys
import io, os
input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline

n, m, k = map(int, input().split())
g = [[] for i in range(n)]
for i in range(m):
    a, b, c = map(int, input().split())
    a, b = a-1, b-1
    g[a].append((c, b))
    g[b].append((c, a))
D = list(map(int, input().split()))
dp = [True]*n
for i, d in enumerate(D):
    nx = [False]*n
    for v in range(n):
        if not dp[v]:
            continue
        for c, u in g[v]:
            if c == d:
                nx[u] = True
    dp = nx
ans = []
for v in range(n):
    if dp[v]:
        ans.append(v+1)
print(len(ans))
print(*ans)