Arizona Cardinals rookie receiver John Brown scored on a 13-yard pass from Carson Palmer with 2:25 left in the game to defeat San Diego 18-17 on Monday night. The Chargers led 17-6 after three periods, but did not convert on multiple opportunities throughout the game. It was the fifth loss for San Diego over the prior three seasons in which they led by a touchdown or more in the fourth quarter, tied for the most in the NFL. Rookie Jeremiah Attaochu set up the Chargers only first-half score with a blocked punt off Drew Butler. San Diego trailed 6-3 at halftime when Chargers quarterback Philip Rivers went 6-for-6 for 82 yards and threw a 6-yard touchdown to Malcom Floyd for a 10-6 lead. Attaochu forced a Palmer fumble on a strip sack to set up a 20-yard touchdown run by Ryan Mathews for a 17-6 Charger advantage. The Cardinals pulled to 17-12 after a 10-play, 64-yard touchdown drive with 12:30 remaining; their two-point conversion failed. On San Diego's following drive, they were in field-goal range at the Arizona 29-yard line when a mishandled snap from backup center Rich Ohrnbergerreplacing an injured Nick Hardwick who left the gameto Rivers pushed the Chargers back to the 43 and forced a punt. Arizona then went on their 11-play, 91-yard game-winning drive, which was extended by a slow-footed Palmer scrambling 12 yards on a third-and-10 play. The Chargers offense, which ranked fifth in the NFL in yards in 2013, suffered from uncharacteristic dropped passes. Arizona's late field goal in the second quarter came after a Chargers interception set up by Eddie Royal stopping on his route as a Rivers pass went to the Chiefs Jerraud Powers. The Chargers' Marcus Gilchrist dropped an apparent sure interception in the third quarter.

Based on the above article, answer a question. How many points ahead were the Cardinals at halftime
3