var
  n,i:longint;
  cur,tot:double;
begin
  readln(n);
  cur:=420000.00/n;
  tot:=0;  
  for i:=1 to n-1 do begin
    tot:=tot+cur;
    cur:=cur*(2*double(i)-1)/(2*double(i))
  end;
  writeln(tot+cur:0:2);
  close(input);
  close(output);
end.