var f1,f2:text;
    n:longint;
begin
        assign(f1,'oras.in');
        reset(f1);
        assign(f2,'oras.out');
        rewrite(f2);
        read(f1,n);
        if n mod 2=0 then
                writeln(f2,-1);
        close(f1);
        close(f2);
end.