Profits fell from a high of DM330,000,000 in 1969 to DM12,000,000 in 1971, mainly due to slumping Beetle sales and high R&D costs. In 1971 the United States' government ended international convertibility of the US dollar to gold in what is termed the Nixon shock. One outcome of this was that the Deutsche Mark rose 40 percent against the US dollar in 1971. This, combined with a 10% import duty on cars entering the US, caused Beetle sales to plummet in what had become a critical market for Volkswagen. In 1973 the OPEC oil crisis hit, triggering a global recession. The German government responded with emergency measures banning private car use on certain days of the week and comprehensive speed limits. In 1972 Opel's share of the German market rose to 20.4%, making them Germany's largest automobile manufacturer and overtaking Volkswagen in their domestic market. In 1972 the Center for Auto Safety published "Small--on safety: the designed-in dangers of the Volkswagen", which examined the safety deficiencies of the Beetle just as Ralph Nader's earlier book "Unsafe at Any Speed" had done for the Chevrolet Corvair. All of the foregoing combined to result in Volkswagen posting a DM807,000,000 loss in 1974. In the same year Volkswagen of America alone posted a DM200,000,000 loss. Rudolf Leiding replaced Lotz as Director General of Volkswagen from 1971 to 1975. Commenting on the situation at Volkswagen as he found it, Leiding said: "The global situation for VW was more critical than we had once thought - to put it simply, we were dealing with the survival of a giant group, which employed more than 220,000 people worldwide ..." Two weeks after assuming the directorship, Leiding stopped work on the Porsche-designed EA266 and ordered all but two of the 50 prototypes built to that point to be destroyed. In 1969 Lotz and Italian Volkswagen importer Gerhard R. Gumpert visited the Turin Auto Show. After selecting their six favourite cars of the show, they discovered that four of the six were designed by Giorgetto Giugiaro and his Italdesign studio. Giugiaro was invited to Wolfsburg in January 1970 to work on development project EA337. The design brief provided by Volkswagen specified a C-segment car with a two-box body in three- and five-door versions. The client also provided Giugiaro with the basic dimensions and the power-train options. Giugiaro produced a design that reflected his signature "origami" or "folded-paper" style, emphasizing sharp corners and flat planes.