SP1437 PT07Z - Longest path in a tree

You are given an unweighted, undirected tree. Write a program to output the length of the longest path (from one node to another) in that tree. The length of a path in this case is number of edges we traverse from source to destination.

The first line of the input file contains one integer $N$ --- number of nodes in the tree ($0< N \le 10^4$). Next $N-1$ lines contain $N-1$ edges of that tree --- Each line contains a pair $(u,v)$ means there is an edge between node $u$ and node $v$.

Print the length of the longest path on one line.