Domino
Togrul has created a simple game for you to test your skills. The objective is to determine the length of the longest chain that can be formed using a given set of dominoes.
Each domino is represented by a pair of numbers a and b, indicating the number of dots on each half of the domino. A valid chain is a sequence of dominoes arranged in a line such that for any two consecutive dominoes with indices i and i+1, the condition b[i] = a[i+1] is satisfied.
To find the solution, Togrul asks you to write a program that calculates the length of the longest possible chain.
Input
The first line contains an integer n (1 <= n <= 100,000), representing the number of dominoes.The next n lines each contain two integers a[i] and b[i] (0 <= a[i] <= b[i] <= 10^9), describing the dominoes.
Output
Output a single integer on one line, which is the maximum length of the domino chain.