Context: After a tough loss to the Jets, the Steelers traveledto LP Field to take on the Titans.  In the first quarter, the Steelers scored first when Shaun Suisham kicked a 49-yard field goal for a 3-0 lead.  They increased their lead as William Gay picked off Zach Mettenberger and returned it 28 yards for a TD for a 10-0 lead.  The Titans finally got on the board when Bishop Sankey ran for a 9-yard TD for a 10-7 game.  However, the Steelers pulled away as Suisham kicked another field goal from 23 yards out for a 13-7 lead.  In the 2nd quarter, it was all Titans when Ryan Succop kicked a 20-yard field goal to come within 3, 13-10.  They eventually took the lead when Mettenberger found Nate Washington on an 80-yard TD pass and led the game 17-13 at halftime.  After the break, the Titans went back to work in the 3rd quarter with Mettenberger finding Chase Coffman on a 4-yard TD pass for a 24-13.  In the 4th quarter, the Steelers staged a comeback when Le'Veon Bell ran for a 5-yard TD to come within 4, 24-20.  Then Roethlisberger found Antonio Brown on a 12-yard TD pass later on in the quarter to retake the lead 27-24.  The defense was able to hold off the Titans offense and recovered the onside kick with less than 2 minutes remaining, sending the Steelers to 7-4 going into their bye week. Le'Veon Bell ran for 204 yards, an NFL high for a single game so far in 2014. It was also the best game by a Steelers running back since 2010. This was the Steelers' only game outside of the Eastern Time Zone time zone during the 2014 season.

Question: How many points were the Titans leading by at halftime?

Answer:
4