var s,i,n:longint;
begin
     assign(input,'fractii.in');
     reset(input);
     assign(output,'fractii.out');
     rewrite(output);
     readln(n);
     if n=1 then writeln(1)
     else
     if n=2 then writeln(2)
     else
     if n=3 then writeln(7)
     else
     begin
          s:=7;
          for i:=4 to n do
          begin
               if i mod 2=0 then
               begin
                    s:=s+i;
                    if (i div 2) mod 2=1 then
                         s:=s-2
               end
               else
               begin
                    s:=s+2*i-2;

               end;
          end;
          writeln(s);
     end;

close(output);
end.