 Complete the following phrase:  After winning eighty races as an amateur racer, he turned professional on 29 April 1965 when he signed with . His first major victory came in the MilanSan Remo a year later, after switching to . After the 1967 season, Merckx moved to , and won the Giro dItalia, his first Grand Tour victory. Four times between 1970 and 1974, Merckx completed a Grand Tour double. His final double also coincided with winning the mens road race at the 