program Fractii;
var
   Fl : text;
   n, i, j, k, s : longint;

function max1(in1, in2 : longint) : longint;
begin
   max1 := in1;
   k := in2;
   if in1 < in2 then
      begin
         k := in1;
         max1 := in2;
      end;

end;
begin
   Assign(Fl,'fractii.in');
   Reset(Fl);
   ReadLn(Fl,n);
   close(Fl);

   s := n;
   for i := 2 to n do
      for j := 1 to n do
         if (max1(i,j) mod k > 0) and ((i mod 2 = 1) or (j mod 2 = 1)) then
            begin
               s := s + 1;
               WriteLn(i,' ',j);
            end;

   s := s + n - 1;

   Assign(Fl,'fractii.out');
   ReWrite(Fl);
   WriteLn(Fl,s);
   Close(Fl);

   ReadLn;
end.