Task: Question Answering
Input (English): Passage: The Chargers defeated the Kansas City Chiefs 37-20 and started the season with a 3-1 record for the second consecutive year.  San Diego forced the Chiefs into six turnovers, and they led 20-0 in the second quarter. Rivers completed 18 of 23 passes for 209 yards and two touchdown passes, but threw one interception in the red zone. Jackie Battle started at running back instead of Mathews. Battle was in 27 plays compared to Mathews' 21, and he had 15 carries for 39 yards with a team-high four catches for 42 yards. Most of Mathews work was in the fourth quarter when San Diego's victory was mostly already decided. U-T San Diego wrote that Mathews would have been expected to start were it not for his fumble against Atlanta the prior week. Nick Novak filled in for kicker Nate Kaeding, who was out with a groin injury, and made all three of his field goals. 
Question: How many passes did Rivers fail to complete? 
Answer type: Number 
Output (English): 5.