Question: In what year did the historical film drama based on the true story of Charles Horman win The Palme d'Or?

full_context: Document 1: 2014 Cannes Film Festival: The 67th Cannes Film Festival was held from 14 to 25 May 2014. New Zealand film director Jane Campion was the head of the jury for the main competition section. The Palme d'Or was awarded to the Turkish film "Winter Sleep" directed by Nuri Bilge Ceylan.
Document 2: 1955 Cannes Film Festival: The 8th Cannes Film Festival was held from 26 April to 10 May 1955. The Golden Palm went to the US film "Marty" by Delbert Mann. The festival opened with "Du rififi chez les hommes" by Jules Dassin and closed with "Carmen Jones" by Otto Preminger.
Document 3: Joyce Horman: Joyce Marie Horman (born December 3, 1944) is an American human rights activist. She is known as the wife of journalist Charles Horman, who went missing in 1973 while the couple was living in Santiago, Chile. Her search for what happened to him was chronicled in the 1982 film "Missing", in which she was portrayed by Sissy Spacek. Spacek was nominated for an Academy Award for her performance as Horman. Her family's story was first told in the 1978 book by Thomas Hauser titled "The Execution of Charles Horman: An American Sacrifice".
Document 4: Missing (1982 film): Missing (stylized as missing.) is a 1982 American historical drama film directed by Costa-Gavras and starring Sissy Spacek, Jack Lemmon, Melanie Mayron, John Shea, Janice Rule and Charles Cioffi. It is based on the true story of American journalist Charles Horman, who disappeared in the bloody aftermath of the US-backed Chilean coup of 1973 that deposed the democratically elected socialist President Salvador Allende. Set largely during the days and weeks following Horman's disappearance, the movie depicts his father and wife searching to determine his fate. The film examines the relationship between Horman's wife Beth (Spacek) and her father-in-law, American businessman Ed Horman (Lemmon).
Document 5: 2007 Cannes Film Festival: The 60th Cannes Film Festival ran from 16 to 27 May 2007. The President of the Jury was British director Stephen Frears. Twenty two films from twelve countries were selected to compete for the Palme d'Or. The awards were announced on 26 May. "4 Months, 3 Weeks and 2 Days", directed by Cristian Mungiu won the Palme d'Or.
Document 6: 1986 Cannes Film Festival: The 39th Cannes Film Festival was held from 8 to 19 May 1986. The Palme d'Or went to "The Mission" by Roland Joffé.
Document 7: Elizabeth Horman: Elizabeth Dorothy Horman (December 30, 1904 – May 10, 2001) was an American fine-artist. She was also known as the wife of businessman Edmund Horman, and the mother of Charles Horman, a journalist that was killed in Chile in 1973. The events of her son's death were chronicled in the 1982 film "Missing".
Document 8: The Missing (TV series): The Missing is a British television drama series written by brothers Harry and Jack Williams first broadcast on BBC One in the UK on 28 October 2014 and in the US on Starz on 15 November 2014. The first eight-part series was about the search for a missing boy in France, and was directed by Tom Shankland. It stars Tchéky Karyo as Julien Baptiste, the French detective who leads the case with James Nesbitt and Frances O'Connor as the boy's parents. "The Missing" is a co-production between the BBC and Starz.
Document 9: The Official Story: The Official Story (Spanish: "La historia oficial" ) is a 1985 Argentine drama historical film directed by Luis Puenzo and written by Puenzo and Aída Bortnik. It stars Norma Aleandro, Héctor Alterio, Chunchuna Villafañe and Hugo Arana. In the United Kingdom, it was released as "The Official Version".
Document 10: No (2012 film): No is a 2012 internationally co-produced historical drama film directed by Pablo Larraín. The film is based on the unpublished play "El Plebiscito", written by Antonio Skármeta. Mexican actor Gael García Bernal plays René, an in-demand advertising man working in Chile in the late 1980s. The film captures the historical moment of advertising tactics in political campaigns as in the 1988 plebiscite, when the Chilean citizenry decided whether or not dictator Augusto Pinochet should stay in power for another eight years.
Document 11: 1982 Cannes Film Festival: The 35th Cannes Film Festival was held from 14 to 26 May 1982. The Palme d'Or was jointly awarded to "Missing" by Costa Gavras and "Yol" by Şerif Gören and Yılmaz Güney.
Document 12: 1958 Cannes Film Festival: The 11th Cannes Film Festival was held from 2 to 18 May 1958. The Palme d'Or went to the "Letyat zhuravli" by Mikhail Kalatozov.
Document 13: 1987 Cannes Film Festival: The 40th Cannes Film Festival was held from 7 to 19 May 1987. The Palme d'Or went to the "Sous le soleil de Satan" by Maurice Pialat, a choice which was considered "highly controversial" and the prize was given under the jeers of the public. Pialat is quoted to have retorted "You don’t like me? Well, let me tell you that I don’t like you either!"
Document 14: 1961 Cannes Film Festival: The 14th Cannes Film Festival was held from 3 to 18 May 1961. The Palme d'Or went to the "Une aussi longue absence", directed by Henri Colpi and "Viridiana", directed by Luis Buñuel. The festival opened with "Che gioia vivere", directed by René Clément.
Document 15: Salvador Allende (film): Salvador Allende is a 2004 documentary film about Chilean president Salvador Allende, from his election campaign to the "coup d'état" which ended his life. It was directed by Patricio Guzmán and screened out of competition at the 2004 Cannes Film Festival.
ground_truth: 1982