def main():
    n, m, k = map(int, input().split())

    paths = []
    for _ in range(m):
        a, b, c = map(int, input().split())
        paths.append([a, b, c])
    d = [0] + list(map(int, input().split()))

    # dp[i][j]=(i回の移動後に街jにいる可能性があるかどうか)
    dp = [[False] * (n + 1) for _ in range(k + 1)]
    # 1回目
    for a, b, c in paths:
        if c == d[1]:
            dp[1][a] = True
            dp[1][b] = True

    # 2回目以降
    for i in range(2, k + 1):
        for a, b, c in paths:
            if c == d[i]:
                if dp[i - 1][a]:
                    dp[i][b] = True
                if dp[i - 1][b]:
                    dp[i][a] = True

    ans = [i for i in range(1, n + 1) if dp[k][i]]
    print(len(ans))
    print(*ans)


if __name__ == "__main__":
    main()