2
3 4
this_is_a_document_that_contains_many_underscores
_this_is_another_document_which_contains_even_more_underscores_
thethirddocumentdoesnotcontainanyunderscoresatall
2 underscore document
2 is_ even_more
3 does not contain
2 contain any
1 2
blablabla
3 bla bla blabla
1 blahblah