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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<iostream>
#include<algorithm>
using namespace std;
int arr[200000]={0};
struct stu{
    int x;
    int y;
};
struct stu z[100005];
bool com(struct stu a,struct stu b){
    if(a.y==b.y){
        return a.x < b.x;
    }
    else{
        return a.y < b.y;
    }
}
int main()
{
	int a,b,c,i,n,m;
	int j;
	cin>>m>>n;
	for(i = 1;i <= n;i++){
        cin>>z[i].x>>z[i].y;
	}
	sort(z,z+n,com);
	int now = 0;
	int ans = 0;
	for(i = 1;i <= n;i++){
        if(z[i].x >= now){
            ans++;
            now = z[i].y;
        }
	}
	cout<<ans;
}