<Tr> <Td> 07 </Td> <Td> Homicide: Life on the Street </Td> <Td> NBC </Td> <Td> 1993 - 01 - 31 </Td> <Td> 1999 - 05 - 21 </Td> <Td> 122 </Td> </Tr> <Tr> <Td> 07 </Td> <Td> Cheyenne </Td> <Td> ABC </Td> <Td> 1955 - 09 - 20 </Td> <Td> 1962 - 12 - 17 </Td> <Td> 108 </Td> </Tr> <Tr> <Td> 07 </Td> <Td> Rules of Engagement </Td> <Td> CBS </Td> <Td> 2007 - 02 - 05 </Td> <Td> 2013 - 05 - 20 </Td> <Td> 100 </Td> </Tr> <Tr> <Td> 07 </Td> <Td> The Walking Dead </Td> <Td> AMC </Td> <Td> 2010 - 10 - 31 </Td> <Td> Present </Td> <Td> 99 </Td> </Tr>

What is the longest running television show in us history