The Diameter of the Empire

Sheldor's Empire forms a graph with cities as vertices and edges as roads. All the roads in his empire are of unit distance. He defines the diameter of the Empire as the maximum distance between two cities in his empire.

What is the diameter of his empire?

Input File: Link

Input Constraints and Details:

• The empire contains of 100 cities.
• Each line in the Input File contains two integers $u$ and $v$ . This refers to the fact that there is a road connecting $u$ and $v$ .