Problem Statement

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.