I have following file content (3 fields each line):

23 888 10.0.0.1
dfh 787 10.0.0.2
dssf dgfas 10.0.0.3
dsgas dg 10.0.0.4
df dasa 10.0.0.5
df dag 10.0.0.5
dfd dfdas 10.0.0.5
dfd dfd 10.0.0.6
daf nfd 10.0.0.6
...

as can be seen, that the third field is ip address and sorted. but there is duplilcate ip addresses. I want to kill line 6,7 and 9, so the new file will be

23 888 10.0.0.1
dfh 787 10.0.0.2
dssf dgfas 10.0.0.3
dsgas dg 10.0.0.4
df dasa 10.0.0.5
dfd dfd 10.0.0.6
...

please tell me how to do this, thanks!