There are N islands lining up from west to east, connected by N-1 bridges. The i-th bridge connects the i-th island from the west and the (i+1)-th island from the west. One day, disputes took place between some islands, and there were M requests from the inhabitants of the islands: Request i: A dispute took place between the a_i-th island from the west and the b_i-th island from the west. Please make traveling between these islands with bridges impossible. You decided to remove some bridges to meet all these M requests. Find the minimum number of bridges that must be removed.

-----Constraints-----

• All values in input are integers.
• 2 \leq N \leq 10^5
• 1 \leq M \leq 10^5
• 1 \leq a_i < b_i \leq N
• All pairs (a_i, b_i) are distinct.

-----Input----- Input is given from Standard Input in the following format: N M a_1 b_1 a_2 b_2 : a_M b_M

-----Output----- Print the minimum number of bridges that must be removed.

-----Sample Input----- 5 2 1 4 2 5

-----Sample Output----- 1

The requests can be met by removing the bridge connecting the second and third islands from the west.