Problem:
Score : 400 points

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.

Sample Input 1

5 2
1 4
2 5

Sample Output 1

1

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

Sample Input 2

9 5
1 8
2 7
3 5
4 6
7 9

Sample Output 2

2

Sample Input 3

5 10
1 2
1 3
1 4
1 5
2 3
2 4
2 5
3 4
3 5
4 5

Sample Output 3

4

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.ArrayList;
import java.util.Comparator;
import java.util.Scanner;

public class Main 
{
	static class C implements Comparator<Req>
	{
		@Override
		public int compare(Req o1, Req o2) 
		{
			return o1.r - o2.r;
		}
	}
	
	static class Req
	{
		boolean done = false;
		int l;
		int r;
		
		public Req(int l0, int r0)
		{
			l = l0;
			r = r0;
		}
	}
	

	public static void main(String[] args) 
	{
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();


		ArrayList<Req> list = new ArrayList<Req>();
		
		for(int i = 0; i < m; i++)
		{
			int a = sc.nextInt()-1;
			int b = sc.nextInt()-1;
			list.add(new Req(a,b));
		}
		
		C c = new C();
		list.sort(c);
		
		int dn = 0;
		
		int destroyedl = -99;
		for(int i = 0; i < m; i++)
		{
			Req cur = list.get(i);
			
//			System.out.println("Do " + cur.l + " " + cur.r + ", desl " + destroyedl);
			if(cur.l >= destroyedl)
			{
//				System.out.println("Right before " + cur.r);
				destroyedl = cur.r;
				dn++;
			}
			
		}
		
		System.out.println(dn);

	}






}