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 (GCC 9.2.1) (judge verdict: Time Limit Exceeded)

#include<stdio.h>

int main(void){
  int n , m;
  scanf("%d %d",&n ,&m);
  
  int a[m] , b[m];
  for(int i = 0;i < m;i ++){
    scanf("%d %d",&a[i] ,&b[i]);
  }

  int temp;
  for(int i = 0;i < m;i ++){
    for(int j = i+1;j < m;j ++){
      if(b[i] > b[j]){
        temp = b[i];
        b[i] = b[j];
        b[j] = temp;
        temp = a[i];
        a[i] = a[j];
        a[j] = temp;  
      }
    }
  }

  int max = 0 , count = 0;
  for(int i = 0;i < m;i ++){
    if(max < a[i]){
      count ++;
      max = b[i] - 1;
    }
  }

  printf("%d\n",count);

  return 0;
}