var x,i,n,m:longint;
ok:boolean;
f,g:text;
begin
assign(f,'dame.in');
assign(g,'dame.out');
reset(f);
rewrite(g);
read(f,n);
writeln(g,n);
if n mod 2=1 then begin
 m:=n div 2+1;
 for i:=1 to m do
  writeln(g,i*2-1,' ',m-i+1);
 for i:=1 to m-1 do
  writeln(g,i*2,' ',n-i+1);
end
else
begin
 m:=n div 2;
 for i:=1 to m do
  writeln(g,i*2-1,' ',m-i+1);
  ok:=true;
 for i:=1 to m do begin
  ok:=not ok;
  x:=n-i+1;
  if ok then inc(x) else dec(x);
  writeln(g,i*2,' ',x);
 end;
end;
close(f);
close(g);
end.