In August 2003, Spears opened the MTV Video Music Awards with Christina Aguilera, performing "Like a Virgin". Halfway through they were joined by Madonna, with whom they both kissed. The incident was highly publicized. In 2008, MTV listed the performance as the number-one opening moment in the history of MTV Video Music Awards, while Blender magazine cited it as one of the twenty-five sexiest music moments on television history. Spears released her fourth studio album, In the Zone, in November 2003. She assumed more creative control by writing and co-producing most of the material. Vibe called it "A supremely confident dance record that also illustrates Spears's development as a songwriter." NPR listed the album as one of "The 50 Most Important Recording of the Decade", adding that "the decade's history of impeccably crafted pop is written on her body of work." In the Zone sold over 609,000 copies in the United States during its first week of availability in the United States, debuting at the top of the charts, making Spears the first female artist in the SoundScan era to have her first four studio albums to debut at number one. It also debuted at the top of the charts in France and the top ten in Belgium, Denmark, Sweden and the Netherlands. In the Zone sold over 10 million copies worldwide. The album produced four singles: "Me Against the Music", a collaboration with Madonna; "Toxic"—which won Spears her only Grammy for Best Dance Recording; "Everytime" and "Outrageous".In January 2004, Spears married childhood friend Jason Allen Alexander at A Little White Wedding Chapel in Las Vegas, Nevada. The marriage was annulled 55 hours later, following a petition to the court that stated that Spears "lacked understanding of her actions".In March 2004, she embarked on The Onyx Hotel Tour in support of In the Zone. In June 2004, Spears fell and injured her left knee during the music video shoot for "Outrageous". Spears underwent arthroscopic surgery. She was forced to remain six weeks with a thigh brace, followed by eight to twelve weeks of rehabilitation, which caused The Onyx Hotel Tour to be canceled.During 2004, Spears became involved in the Kabbalah Centre through her friendship with Madonna.In July 2004, Spears became engaged to American dancer Kevin Federline, whom she had met three months before. The romance received intense attention from the media, since Federline had recently broken up with actress Shar Jackson, who was still pregnant with their second child at the time. The stages of their relationship were chronicled in Spears's first reality show Britney & Kevin: Chaotic. They held a wedding ceremony on September 18, 2004, but were not legally married until three weeks later on October 6 due to a delay finalizing the couple's prenuptial agreement. Shortly after, she released her first perfume with Elizabeth Arden, Curious, which broke the company's first-week gross for a perfume. In October 2004, Spears took a career break to start a family. Greatest Hits: My Prerogative, her first greatest hits compilation album, was released in November 2004. Spears's cover version of Bobby Brown's "My Prerogative" was released as the lead single from the album, reaching the top of the charts in Finland, Ireland, Italy and Norway. The second single, "Do Somethin'", was a top ten hit in Australia, the United Kingdom and other countries of mainland Europe. In August 2005, Spears released "Someday (I Will Understand)", which was dedicated to her first child, a son, who was born the following month. In November 2005, she released her first remix compilation, B in the Mix: The Remixes, which consists of eleven remixes. It has sold over 1 million copies worldwide.

Question: How many copies were sold?
Answer: over 10 million