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 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <math.h>

int main ()
{
    
    int N =0,M=0,count = 0;
    scanf("%d %d",&N,&M);
    
    int a[M],b[M];
    for(int i = 0;i<M;i++)
    {
    
    scanf("%d %d",&a[i],&b[i]);
        
    }
    
    for(int i = 0;i<M;i++)
    {
        for(int j = M;j>i;j--)
        {
            if(a[j]<a[j-1])
            {
                int c = a[j],d = b[j];
                
                a[j] = a[j-1];
                b[j] = b[j-1];
                
                a[j-1] = c;
                b[i-1] = d;
                
                
            }
        }
    }
    
    
    for(int i = 0;i<M;i++)
    {
        for(int j = M;j>i;j--)
        {
            if((b[j]<b[j-1])&&(a[j] == a[j-1]))
            {
                int c = a[j],d = b[j];
                
                a[j] = a[j-1];
                b[j] = b[j-1];
                
                a[j-1] = c;
                b[i-1] = d;
                
                
            }
        }
    }
    int ca= a[0],cb = b[0];
    
    for(int i = 0;i<M;i++){
        
        if(a[i+1]<cb){
            
            if(cb>b[i+1])
            cb=b[i+1];
            
        }
        
        
        
        else{
            ca=a[i+1];
            cb= b[i+1];
            count++;
        }
        
        
    }
        
    printf("%d\n",count);
    
    
    return 0;
}