var n,s,m,i,nn:longint;
    f:text;
    begin
    assign(f,'fractii.in');
    reset(f);
    read(f,n);
    close(f);
    s:=n*2;
    if n mod 2=0 then m:=n div 2
                 else m:=(n div 2)+1;
    nn:=n;
    i:=1;
    n:=n-1;
    while i<=nn-3 do
    begin
    if i mod 2<>0 then s:=s+m
                  else begin s:=s+n;
                             dec(n);
                             end;
      inc(i);
    end;
    assign(f,'fractii.out');
    rewrite(f);
    write(f,s+1);
    close(f);
    end.