LAS VEGAS : Seven times Formula One world champion Lewis Hamilton said on Wednesday he had felt like walking away from Mercedes after a tough race in Brazil this month. The 39-year-old Briton, the sport's most successful driver, is joining Ferrari at the end of the year and hinted over team radio in Sao Paulo that he might be leaving the team ahead of time. The comments were played down by Mercedes as aimed at team members who would not be at the last three rounds, but Hamilton told reporters