program dame;
var n,lv,i:longint;
        f,g:text;
        v:array[1..2001] of longint;





procedure iofile;
var i,p,aux:longint;
begin
        assign(f,'dame.in');
        reset(f);
        assign(g,'dame.out');
        rewrite(g);
        readln(f,n);
        if (n=0)or(n>=4) then writeln(g,n);
        close(f);
        if (n=1) then
                begin
                        writeln(g,'1');
                        writeln(g,'1 1');
                        close(g);
                        halt;
                end else if n=2 then
                        begin
                        writeln(g,'1');
                        writeln(g,'1 1');
                        close(g);
                        halt;
                        end;
                if n=3 then
                        begin
                                writeln('2');
                                writeln(g,'1 1');
                                writeln(g,'3 2');
                                close(g);
                                halt;
                        end;
        for i:=1 to n div 2 do
                begin
                        inc(lv);
                        v[lv]:=i*2;
                end;
        if n mod 12 in [3,9] then
                begin
                        for i:=1 to lv-1 do
                                v[i]:=v[i+1];
                        v[lv]:=2;
                end;
        for i:=1 to n div 2 do
                begin
                        inc(lv);
                        v[lv]:=i*2-1;
                end;
        if n mod 2=1 then
                begin
                        inc(lv);
                        v[lv]:=n;
                end;
        if n mod 12=8 then
                begin
                        i:=n div 2+1;
                        while i+1<=n do
                                begin
                                        aux:=v[i];
                                        v[i]:=v[i+1];
                                        v[i+1]:=aux;
                                        inc(i,2);
                                end;
                end else
        if n mod 12=2 then
                begin
                        aux:=v[n div 2+1];
                        v[n div  2+1]:=v[n div 2+2];
                        v[n div 2+2]:=aux;
                        p:=n div 3+3;
                        for i:=p to n-1 do
                                v[i]:=v[i+1];
                        v[n]:=5;
                end else
        if n mod 12 in [3,9] then
                begin
                        for i:=n div 2+1 to n-2 do
                                v[i]:=v[i+2];
                        v[n-1]:=1;
                        v[n]:=3;
                end;


end;




begin
        iofile;
        for i:=1 to n do
                writeln(g,i,' ',v[i]);
        close(g);
end.