You don’t, you have the option to say “Neither”, or “Prefer not to say” and we are happy with that. We use this data to get a picture of what the National Cipher Challenge community looks like and don’t store it with your registration info. We recognise that “Neither” could look a bit dismissive and we did consider a range of other options, but in practice we don’t need to know so probably shouldn’t be asking, though that might change in the future.