Solve the programming task below in a Python markdown code block.
Read problems statements in Mandarin Chinese  and Russian. 

N one dimensional kingdoms are represented as intervals of the form [a_{i} , b_{i}] on the real line.
A kingdom of the form [L, R] can be destroyed completely by placing a bomb at a point x on the real line if L 
≤ x ≤ R.

Your task is to determine minimum number of bombs required to destroy all the one dimensional kingdoms.

------ Input ------ 

First line of the input contains T denoting number of test cases.

For each test case, first line contains N denoting the number of one dimensional kingdoms.

For each next N lines, each line contains two space separated integers a_{i} and b_{i}.

------ Output ------ 

For each test case , output an integer denoting the minimum  number of bombs required.

------ Constraints ------ 

Subtask 1 (20 points) : 1 ≤ T ≤ 100 , 1 ≤ N ≤ 100 , 0 ≤ a_{i} ≤ b_{i} ≤500  
Subtask 2 (30 points) : 1 ≤ T ≤ 100 , 1 ≤ N ≤ 1000 , 0 ≤ a_{i} ≤ b_{i} ≤ 1000   
Subtask 3 (50 points) : 1 ≤ T ≤ 20 , 1 ≤ N ≤ 10^{5}, 0 ≤ a_{i} ≤ b_{i} ≤ 2000 

----- Sample Input 1 ------ 
1
3
1 3
2 5
6 9
----- Sample Output 1 ------ 
2
----- explanation 1 ------ 
There are three kingdoms [1,3] ,[2,5] and [6,9]. You will need at least 2 bombs 
to destroy the kingdoms. In one of the possible solutions, you can place two bombs at x = 2 and x = 6 .