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: Wrong Answer)

import java.util.*;
import java.io.*;

public class Main{
	public static void main(String[] args){

	Scanner stdIn = new Scanner(System.in);
	BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
	
	int n = stdIn.nextInt();
	int m = stdIn.nextInt();

	int[] lpoint = new int[m];
	int[] rpoint = new int[m];

	int ans = 1;
	for(int i = 0;i < m;i++){
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();

		if(i > 0){
			for(int j = 0;j < i;j++){
				if(rpoint[j] < a || lpoint[j] > b){
					ans++;
					break;
				}
			}
		}
			
		lpoint[i] = a;
		rpoint[i] = b;
	}
	System.out.println(ans);
		
	}
}