var  f,g:text;
     i,j,n,c:longint;
     a:array[1..100,1..100] of 0..1;
begin
assign(f,'dame.in'); reset(f);
assign(g,'dame.out'); rewrite(g);
read(f,n);
writeln(g,n);
if n mod 2=0 then c:=n div 2
             else c:=n div 2+1;
i:=1;
for j:=1 to c do begin
                 writeln(g,i,' ',j);
                 inc(i,2);
                 end;
i:=2;
for j:=c+1 to n do begin
                   writeln(g,i,' ',j);
                   inc(i,2);
                   end;
{for i:=1 to n do begin
for j:=1 to n do write(g,a[i,j],' ');
writeln(g);
end; }
close(g);
end.