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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int N=sc.nextInt();
		int M=sc.nextInt();
		int B[]=new int[M];
		int C[]=new int[M];
		int f=0;
		int ans=1;
		for(int i=0;i<M;i++) {
			B[i]=sc.nextInt();
			C[i]=sc.nextInt();
		}
		for(int i=0;i<M-1;i++) {
			int d=C[i];
			int e=i;
			for(int k=i+1;k<M;k++) {
				if(d>C[k]) {
					d=C[k];
					e=k;
				}
			}
			f=B[e];
			B[e]=B[i];
			B[i]=f;
			f=C[e];
			C[e]=C[i];
			C[i]=f;
		}
		for(int i=0;i<M;i++) {
			System.out.println(B[i]);
			System.out.println(C[i]);
		}
		int g=C[0];
		for(int i=0;i<M;i++) {
			if(B[i]>=g) {
				ans=ans+1;
				g=C[i];
			}
		}
		System.out.println(ans);
	}
}