Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
United Kingdom railway station categories
Table title:
Categorisation scheme
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=2 rowspan=1 > Category </th><th colspan=1 rowspan=1 > Number (2011) </th><th colspan=1 rowspan=1 > Description </th><th colspan=1 rowspan=1 > Trips per annum </th><th colspan=1 rowspan=1 > Examples </th></tr>
<tr> <td class="highlighted"  colspan=2 rowspan=1 > A </td><td colspan=1 rowspan=1 > 28 </td><td colspan=1 rowspan=1 > National hub </td><td colspan=1 rowspan=1 > over 2 million </td><td colspan=1 rowspan=1 > Birmingham New Street, London King's Cross </td></tr>
<tr> <td class="highlighted"  colspan=2 rowspan=1 > B </td><td colspan=1 rowspan=1 > 67 </td><td colspan=1 rowspan=1 > Regional interchange </td><td colspan=1 rowspan=1 > over 2 million </td><td colspan=1 rowspan=1 > Clapham Junction, Preston </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=2 > C </td><td class="highlighted"  colspan=1 rowspan=1 > C1 </td><td colspan=1 rowspan=2 > 248 </td><td colspan=1 rowspan=2 > Important feeder </td><td colspan=1 rowspan=2 > 0.5–2 million </td><td colspan=1 rowspan=1 > Grantham, Plymouth </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > C2 </td><td colspan=1 rowspan=1 > Burgess Hill, Tamworth </td></tr>
<tr> <td class="highlighted"  colspan=2 rowspan=1 > D </td><td colspan=1 rowspan=1 > 298 </td><td colspan=1 rowspan=1 > Medium staffed </td><td colspan=1 rowspan=1 > 0.25–0.5 million </td><td colspan=1 rowspan=1 > Abergavenny, Penrith </td></tr>
<tr> <td class="highlighted"  colspan=2 rowspan=1 > E </td><td colspan=1 rowspan=1 > 679 </td><td colspan=1 rowspan=1 > Small staffed </td><td colspan=1 rowspan=1 > under 0.25 million </td><td colspan=1 rowspan=1 > Boston, Oakham </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=2 > F </td><td class="highlighted"  colspan=1 rowspan=1 > F1 </td><td colspan=1 rowspan=2 > 1,200 </td><td colspan=1 rowspan=2 > Small unstaffed </td><td colspan=1 rowspan=2 > under 0.25 million </td><td colspan=1 rowspan=1 > Beccles, Bishop Auckland </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > F2 </td><td colspan=1 rowspan=1 > Llanfairpwllgwyngyll, Winchelsea </td></tr>
<tr> <th colspan=2 rowspan=1 > Total </th><th class="highlighted"  colspan=1 rowspan=1 > 2,520 </th><th colspan=1 rowspan=1 >  </th><th colspan=1 rowspan=1 >  </th><th colspan=1 rowspan=1 >  </th></tr>
</table>
Question:
How many overall railway stations are there in Great Britain, how many categories are they classified into, and how many categories have subcategories?
Answer:
The 2,520 railway stations in Great Britain are classified into six categories (two of which are each divided into two subcategories).