var ans,i,n,m,j:longint;
     a,b:array[0..1000]of longint;
     al:array[0..10000000]of integer;

procedure work;
var fi:longint;
begin
     fi:=0;
	 fillchar(al,sizeof(al),0);
	 for i:=m downto 1 do 
	     for j:=a[i] to b[i] do begin
			 if al[j]=0 then begin
				 inc(fi);al[j]:=i;
			     end;
			 if fi=n then exit;
			 end;
end;
procedure calc;
var ac:array[0..1000]of boolean;
begin
	 fillchar(ac,sizeof(ac),false);
	 for i:=1 to n do
		 ac[al[i]]:=true;
	 ans:=0;
	 for i:=1 to m do
		 if ac[i] then inc(ans);
end;
begin
	 assign(input,'ha14d.in');
	 assign(output,'ha14d.out');
	 reset(input);
	 rewrite(output);
     readln(n,m);
	 for i:=1 to m do
		 read(a[i],b[i]);
	 work;
	 calc;
	 writeln(ans);
	 close(input);
	 close(output);
end.