The Chargers began their season at Oakland-Alameda County Coliseum for a Week 1 AFL Legacy duel with their AFC West rival, the Oakland Raiders, in the second game of an MNF doubleheader.  In the first quarter, San Diego trailed early as Raiders running back Michael Bush got a 4-yard touchdown run.  The Chargers would strike back in the second quarter as running back LaDainian Tomlinson got a 1-yard touchdown run.  Oakland would respond with kicker Sebastian Janikowski getting a 37-yard field goal.  San Diego would close out the half with kicker Nate Kaeding making a 47-yard field goal. After a scoreless third quarter, the Raiders would retake the lead in the fourth quarter as Janikowski nailed a 35-yard field goal.  The Chargers would take the lead as quarterback Philip Rivers completed a 15-yard touchdown pass to wide receiver Vincent Jackson.  Oakland would respond with quarterback JaMarcus Russell completing a 57-yard touchdown pass to wide receiver Louis Murphy, but San Diego came right back with a 5-yard touchdown run by running back Darren Sproles.
Question: How many yards was the second longest rushing touchdown?
Answer: 4-yard