问题描述：设计一个程序求出完成整项工程至少需要多少时间以及整项工程中的关键活动。

基本要求：

（1）对一个描述工程的AOE网，应判断其是否能够顺利进行。

（2）若该工程能顺利进行，输出完成整项工程至少需要多少时间，以及每一个关键活动所依附的两个顶点、最早发生时间、最迟发生时间。-Problem descr iption: Design a program to complete the whole project at least find the time required and the whole project is a key activity.

Basic requirements:

(1) a descr iption of the project AOE network, should determine whether it can proceed smoothly.

(2) If the project can proceed smoothly, the output to complete the whole project at least the number of times, and each of the key activities of the two vertices of attachment, the earliest time, the latest time of occurrence.