#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int a[10000010]={0};

int main(){
	freopen("ha14d.in","r",stdin);
	freopen("ha14d.out","w",stdout);
int n,b,c,miao,max=1,ya,chang;
cin>>chang>>n;
for(int i=1;i<=n;i++)
{
	cin>>b>>c;
	miao=b;
	if(c>max) {max=c;}
	for(int q=1;q<=c-miao+1;q++,b++)
	{
		a[b]=i;
	}
}
	sort(a+1,a+n+1);
	for(int i=1,w=2;i<max;i++,w=ya+1)
	{ya=w;
	
		for(;w<=max;w++)
		{
			if(a[i]==a[w])
			{
				a[w]=a[max];
				max--;
				w--;
			}
			
		}
	}
	cout<<max<<endl;
	return 0;
}