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()))
dp = [[False] * (N+1) for _ in range(K)]
for i in range(1,N+1):
    for v,c in G[i]:
        if c == d[0]:
            dp[0][v]= True
for i in range(1,K):
    for j in range(1,N+1):
        if dp[i-1][j]:
            for v,c in G[j]:
                if c == d[i]:
                    dp[i][v] = True
ans = 0
for f in dp[K-1]:
    if f:ans += 1
print(ans)
for i in range(1,N+1):
    if dp[K-1][i]:
        print(i,end = " ")
print()