 Complete the following phrase:  Having signed a contract worth a reported 55 million with Mercedes that was due to expire at the conclusion of , Rosberg continued to drive for the team in . During the off-season he sought to correct a body deficiency, which caused him to hold his breath against g-forces in high-speed corners, since he did not want to limit the flow of oxygen to his brain and muscles. Rosberg said the experience of challenging for the Drivers Championship gave him more motivation to beat Hamilton in 2015 and wanted to improve his driving and win the title. After four top-three podium finishes in the first four races, he won in Spain, Monaco and Austria, which came as his overall performance lowered from focusing more on the race than on qualifying; Vettel threatened Rosbergs hold on second overall. Retirements in Italy and Russia and two errors on a wet track at the stopped him from taking the championship, but wins in the final three races in Mexico, Brazil and 