Late Show With David Letterman

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In this photo provided by CBS, talk show host Keith Olbermann, left, chats with host David Letterman on the set of the “Late Show with David Letterman,” Tuesday April 3, 2012 in New York. (AP Photo/CBS, Jeffrey R. Staab)

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FILE - This March 23, 2010 photo shows Jamie Oliver as he leaves a taping of "The Late Show with David Letterman" in New York. (AP Photo/Charles Sykes)

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FILE - In this July 7, 2009 file photo, actor Sacha Baron Cohen dressed as his character Bruno leaves a taping of "The Late Show with David Letterman" in New York. (AP Photo/Charles Sykes, file)

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In this photo released by CBS, New York City Mayor Michael Bloomberg, left, shares a laugh with host David Letterman on the set of the "Late Show with David Letterman," in New York, Wednesday, Sept. 29, 2010. (AP Photo/CBS, John Paul Filo)

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** FILE ** In this Feb. 11, 2009, file photo, actor Joaquin Phoenix arrives for a taping of "The Late Show with David Letterman" in New York. (AP Photo/Charles Sykes, File)

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In this photo released by CBS, U.S. World Cup soccer team midfielder Landon Donovan, left, talks with host David Letterman on the set of the "Late Show with David Letterman," Tuesday, June 29, 2010, in New York. (AP Photo/CBS, Heather Wines)

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ASSOCIATED PRESS In this photo released by CBS, U.S. World Cup soccer team midfielder Landon Donovan, left, talks with host David Letterman on the set of the "Late Show with David Letterman," Tuesday, June 29, 2010, in New York. Donovan, a key player for Major League Soccer's Los Angeles Galaxy, scored three of the U.S. team's five goals in 2010 World Cup, including a last-minute score against Algeria that sent the team into the second round of tournament play.

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** FILE ** David Letterman admits during an October 2009 broadcast of "The Late Show" to having been sexually involved with some female employees. (AP Photo/CBS)