# dp[i] = 街iにいる可能性があればTrue
# O(MK)
import sys
readline = sys.stdin.readline
N,M,K = map(int,readline().split())
G = [[] for i in range(N)]
for _ in range(M):
    a,b,c = map(int,readline().split())
    G[a - 1].append([b - 1, c])
    G[b - 1].append([a - 1, c])

D = list(map(int,readline().split()))
dp = [True] * N
for d in D:
    new_dp = [False] * N
    for v in range(N):
        if not dp[v]:
            continue
        for child,cost in G[v]:
            if cost != d:
                continue
            new_dp[child] = True
    dp = new_dp

ans = []
for i in range(N):
    if dp[i]:
        ans.append(i + 1)
        
print(len(ans))
print(*ans)