#include "stdio.h"

int main()
{
    int l,m,u[100],v[100],i,j,n=1,s;
    scanf("%d %d",&l,&m);
    for(i=0;i<m;i++){
    	scanf("%d %d",&u[i],&v[i]);
	}
	for(i=0;i<m-1;i++){//将u和v按从小到大的顺序排序
		for(j=i+1;j<m;j++){
		if(u[i]>u[j]){
			s=u[i];
			u[i]=u[j];
			u[j]=s;
			s=v[i];
			v[i]=v[j];
			v[j]=s;
		}
	}
	}
	if(u[1]<=v[0])
		n=n+(v[1]-u[0]);
	else
		n=n+(v[0]-u[0])+(v[1]-u[1])+1;
	for(i=0;i<m-2;i++){
	if(u[i+2]<=v[i+1])
		n=n+(v[i+2]-v[i+1]);
	else
		n=n+(v[i+2]-u[i+2])+1;
	}
	printf("%d",l-n);
    return 0;
}