After a huge road win, the Bengals returned home for a game against the Bills.  The Bengals would draw first blood in the first quarter when Andy Dalton found A.J. Green on a 77-yard pass to make it 7-0.  The Bills scored a field goal later on in the quarter when Stephen Hauschka kicked a 31-yard field goal to make it 7-3.  The Bengals moved up by a touchdown in the second quarter when Randy Bullock nailed a 30-yard field goal to make it 10-3.  Though the Bills would tie it up later on in the quarter when Tyrod Taylor connected with Brandon Tate for a 12-yard pass making the score 10-10 at halftime.  In the third quarter, the Bills moved into the lead with another field goal from Hauschka.  This was from 38 yards out to make the score 13-10.  In the fourth quarter, the Bengals retook the lead when Joe Mixon ran for a 5-yard touchdown making it 17-13.  Hauschka got the Bills closer with a 28-yard field goal to make it 17-16.  Though later on, Bullock kicked a 29-yard field goal making the score 20-16.  This would be the eventual final score of the game. With the win, the Bengals went into their bye week at 2-3.
Question: How many points did the Bengals win by?
Answer: 4