ll@n,@m;
int a[m],b[m];
rd((a,b)(m));
ll l=coordcomp(m,a,m,b);
graph g;
g.setDirectEdge(l,m,b,a);
ll d[l]{};
rep(i,1,l){
	d[i]=d[i-1];
	rep[g.edge[i]](c,g.es[i]){
		d[i]>?=d[c]+1;
	}
}
wt(2n-2-d[l-1]);