Pascal :

var n,i,j,max:longint;a,b,f:array[1..50100]of longint;
    procedure sort(l,r: longint);
      var
         i,j,x,y: longint;
      begin
         i:=l;
         j:=r;
         x:=a[(l+r) div 2];
         repeat
           while a[i]<x do
            inc(i);
           while x<a[j] do
            dec(j);
           if not(i>j) then
             begin
                y:=a[i];
                a[i]:=a[j];
                a[j]:=y;
                y:=b[i];
                b[i]:=b[j];
                b[j]:=y;
                inc(i);
                j:=j-1;
             end;
         until i>j;
         if l<j then
           sort(l,j);
         if i<r then
           sort(i,r);
      end;
begin
  read(n);
  for i:=1 to n do read(a[i],b[i]);
  sort(1,n);
  for i:=1 to n do
    begin
      for j:=1 to i-1 do
        if (b[j]<b[i])and(f[j]>f[i]) then f[i]:=f[j];
      inc(f[i]);
    end;
  for i:=1 to n do if f[i]>max then max:=f[i];
  writeln(max);
end.