program p1203t;
const maxt=30000;
type arr1=array [0..maxt] of integer;
     rec=record ts,te:integer; end;
     arr2=array [0..maxt] of rec;
var a:arr1; n:integer; con:arr2;

{$APPTYPE CONSOLE}

procedure init;
var i,ts,te,j,k:integer; t:arr1;
begin
     readln(n); fillchar(t,sizeof(t),0); j:=0;
     for i:=1 to n do
       begin
         readln(ts,te);
         if (ts>te) then begin k:=ts; ts:=te; te:=k; end;
         if (ts=0) then ts:=-1;
         if (t[te]<ts) then t[te]:=ts;
       end;
     for i:=0 to maxt do
       if (t[i]<>0) then
         begin
           inc(j);
           if (t[i]=-1) then t[i]:=0;
           con[j].ts:=t[i]; con[j].te:=i;
         end;
     for i:=0 to maxt do a[i]:=0; n:=j;
end;

procedure solve;
var i,j:integer;
begin
     for i:=1 to n do
       begin
         for j:=(con[i-1].te+1) to con[i].te do a[j]:=a[con[i-1].te];
         if (a[con[i].ts-1]+1>a[con[i].te]) then a[con[i].te]:=a[con
[i].ts-1]+1;
       end;
end;

procedure sout;
begin
     writeln(a[con[n].te]);
end;

begin
     init;
     solve;
     sout;
end.