Unless your sentence breaks follow a hard and fast format, such as two spaces after ending puncutations you'll never have a perfect solution.

The best you'll be able to do is an "in most cases" regex solution.

Quoted text, abbrevations and initials will cause problems.  For example  She said "How are you?"  I said "Fine." Then Mr. J. Smith walked in.

 If the formatting is consistant you should be able to modify Sergei's regex.

Michael 

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Michael

"In theory, theory and practice are the same. In practice, they are not."
Albert Einstein