//poj 1769
//sep9
#include <iostream>
using namespace std;
const int MAXN=100012;
const int MAXX=9999999;
int n,m;
int minv[MAXN*4];
void build(int l,int r,int k)
{
minv[k]=MAXX;
if(l==r)
return ;
int m=(l+r)/2;
build(l,m,2*k);
build(m+1,r,2*k+1);
}
void update(int i,int v,int k,int l,int r)
{
if(minv[k]>v) minv[k]=v;
if(l==r){
return ;
}
int m=(l+r)/2;;
if(i<=m)
update(i,v,2*k,l,m);
else
update(i,v,2*k+1,m+1,r);
}
int query(int from,int to,int k,int l,int r)
{
if(from<=l&&r<=to)
return minv[k];
int m=(l+r)/2;;
if(to<=m)
return query(from,to,2*k,l,m);
else if(from>m)
return query(from,to,2*k+1,m+1,r);
else
return min(query(from,to,2*k,l,m),query(from,to,2*k+1,m+1,r));
}
int main()
{
scanf("%d%d",&n,&m);
build(1,n,1);
update(1,0,1,1,n);
while(m--){
int s,t;
scanf("%d%d",&s,&t);
if(s>=t) continue;
int end=n;//n = t-1,t,...n all acceptable
int v=query(s,end,1,1,n);
update(t,v+1,1,1,n);
}
printf("%d\n",query(n,n,1,1,n));
}
