Task: Question Answering
Input (English): Passage: Amidst mourning with her family, she focused on work to deal with the grief, avoiding any news coverage of her sibling's death. She commented, "it's still important to face reality, and not that I'm running, but sometimes you just need to get away for a second." During this time, she ended her seven-year relationship with Jermaine Dupri.Several months later, Jackson performed a tribute to Michael at the 2009 MTV Video Music Awards, performing their duet "Scream". MTV stated "there was no one better than Janet to anchor it and send a really powerful message." The performance was lauded by critics, with Entertainment Weekly affirming the rendition "as energetic as it was heartfelt".Jackson's second hits compilation, Number Ones (retitled The Best for international releases), was released in November 2009. For promotion, she performed a medley of hits at the American Music Awards, Capital FM's Jingle Bell Ball at London's O2 arena, and The X-Factor. The album's promotional single "Make Me", produced with Rodney "Darkchild" Jerkins, debuted in September. It became Jackson's nineteenth number one on the Hot Dance Club Songs chart, making her the first artist to have number-one singles in four separate decades.Later that month, Jackson chaired the inaugural benefit of amfAR, The Foundation for AIDS Research, held in Milan in conjunction with fashion week. The foundation's CEO stated "We are profoundly grateful to Janet Jackson for joining amfAR as a chair of its first event in Milan.... She brings incomparable grace and a history of dedication to the fight against AIDS." The event raised a total of $1.1 million for the nonprofit organization. 
Question: What is the full name of the first artist to have number-one singles in four separate decades?
Output (English): Janet Jackson.