<Tr> <Td> Ticino </Td> <Td> TI </Td> <Td> 21 </Td> <Td> SZ20 </Td> <Td> CH070 </Td> </Tr> <Tr> <Td> Uri </Td> <Td> UR </Td> <Td> </Td> <Td> SZ21 </Td> <Td> CH062 </Td> </Tr> <Tr> <Td> Vaud </Td> <Td> VD </Td> <Td> 22 </Td> <Td> SZ23 </Td> <Td> CH011 </Td> </Tr> <Tr> <Td> Valais </Td> <Td> VS </Td> <Td> 23 </Td> <Td> SZ22 </Td> <Td> CH012 </Td> </Tr>

What is the 2 letter abbreviation for switzerland