Question: The 5th season of Game of Thrones, premiering in the spring of 2015, ends with "Mother's Mercy", which landmark episode in total?

Context paragraphs:
The Winter of His Content: "The Winter of His Content" is the fourteenth episode of the 25th season of the American animated sitcom "The Simpsons", and the 544th episode of the series.  It first aired on the Fox network in the United States on March 16, 2014.  It was written by Kevin Curran and directed by Chuck Sheetz.  In the episode, when the Retirement Castle is closed for health violations, Marge invites Grampa and two other old people to live at the Simpsons' house, only to get frustrated with Homer embracing the "old person lifestyle".  Meanwhile, Bart defends Nelson's decision to wear his mother's underwear, and ends up part of a bully gathering a la "The Warriors".

Game of Thrones (season 5): The fifth season of the fantasy drama television series "Game of Thrones" premiered on HBO on April 12, and concluded on June 14, 2015.  It was broadcast on Sunday at 9:00 pm in the United States, consisting of 10 episodes, each running approximately 50–60 minutes.  The season primarily adapts material from "A Feast for Crows" and "A Dance with Dragons", the fourth and fifth novels in George R. R. Martin's "A Song of Ice and Fire" series, though it also uses elements from the third novel, "A Storm of Swords", as well as the upcoming sixth novel "The Winds of Winter".  It also contains original content not found in Martin's novels.  The series is adapted for television by David Benioff and D. B. Weiss.

Survivor Greece 5: Survivor 5 was the 5th season of the Greek version of the popular reality show "Survivor".  The Game started airing on Skai TV on February 13, 2017 in Greece and in Cyprus it started airing the same day on Sigma TV.  It is hosted by Sakis Tanimanidis and two episodes were hosted by the Turkish producer of the Greek version of Survivor, Acun Ilıcalı.  It is also being broadcast abroad via SKAI's international stations.  Twelve players and twelve celebrities have been known in Greece through their work are invited to survive on a deserted island, the exotic Dominican Republic, for 5 months, having their luggage, the necessary clothes and basic food supply.  On episode 77, the last team match took place and on episode 78, individual matches started.  Immunity matches after episode 80 will be held twice a week.  Also, the tribe merge held in episode 44, but individual matches started in episode 78.  The Finals will be held on 3, 4 & 5 July live in the open theatre of Alsos Veikou, Galatsi, Athens.  The winner of season fifth was Giorgos Angelopoulos from the team "Celebrities" (ΔΙΑΣΗΜΟΙ).

Mother's Mercy: "Mother's Mercy" is the tenth and final episode of the fifth season of HBO's fantasy television series "Game of Thrones", and the 50th overall.  The episode was written by the series creators David Benioff and D. B. Weiss and directed by David Nutter.

2015 Guangzhou R&amp;F F.C. season: The 2015 Guangzhou R&F season is the 5th year in Guangzhou R&F's existence and its 5th season in the Chinese football league, also its 4th season in the top flight.

2015–16 1. FSV Mainz 05 season: The 2015–16 1.  FSV Mainz 05 season is the 111th season in the football club's history and 7th consecutive and 10th overall season in the top flight of German football, the Bundesliga, having been promoted from the 2.  Bundesliga in 2009.  In addition to the domestic league, Mainz will also participate in this season's edition of the domestic cup, the DFB-Pokal.  This will be the 5th season for the club in the Coface Arena, located in Mainz, Germany.  The stadium has a capacity of 34,034.  The season covers a period from 1 July 2015 to 30 June 2016.

2015 IFK Norrköping season: The 2015 season was IFK Norrköping's 118th in existence, their 75th season in Allsvenskan and 5th consecutive season in the league.  The club competed in 2015 Allsvenskan, 2014–15 Svenska Cupen (starting with group stage after qualification previous season) and 2015–16 Svenska Cupen (qualification for next season group stage).  The season began with 2014–15 Svenska Cupen group stage on 22 February, with 2015 Allsvenskan starting on 4 April.  The league ended with the last match on 31 October 2015, in which they became league champions, and the last match of the season was 2015 Svenska Supercupen on 8 November where IFK Norrköping, as champions, met 2014–15 Svenska Cupen winners, IFK Göteborg.

1972–73 Carolina Cougars season: The 1972–73 Carolina Cougars season was the 4th season of the Cougars in the American Basketball Association.  The Cougars finished 2nd in points per game with 115.6 points per game and 5th in points allowed with 110.7 points per game.  By the time the season was half over, the team was 28–14, with a season best eleven game winning streak occurring during that span, while they went 29–13 in the second half.  The biggest losing streak was 4, which occurred after they had already won over 50 games.  They clinched the best record in the Eastern Division after beating the San Diego Conquistadors on March 25, 1973, with their 57th victory, is tied for 9th most by a team in one ABA season.  In the playoffs, they beat the New York Nets in five games to go to the Division Finals with a chance to go to the ABA Finals.  But the Cougars failed to advance, losing to the Kentucky Colonels in seven games, with the final one in their home court.

Majisuka Gakuen: Majisuka Gakuen (マジすか学園 ) (lit.  "Majisuka Academy") is a Japanese television drama series first aired on TV Tokyo starring AKB48.  A second season Majisuka Gakuen 2 was aired the following year, the 3rd Season was aired on July 13, 2012.  In 2015, the series moved to NTV and the 4th Season was aired on January 19, 2015.  On the same year, a 5th Season was announced and for the first time will be aired exclusively on internet, by the streaming site Hulu (only in USA & Japan), because NTV will broadcast only the first two episodes (August 24), due to various scenes of violence, which does not justify full season showing on TV, because there may be many problems.  A special spin-off from the 4th and 5th season of the series titled "Majisuka Gakuen 0: Kisarazu Rantōhen" (マジすか学園0 木更津乱闘編 ) (lit.  "Majisuka Academy 0: The story of the Brawl at Kisarazu") which first to feature HKT48 as the main cast and first to have a collaboration with the rock group Kishidan.  It was aired on November 28, 2015 on NTV at 25:05 JST and run for half an hour.

Invasion (Grey's Anatomy): "Invasion" is the fifth episode of the 6th season of the American television medical drama "Grey's Anatomy", and the show's 107th episode overall.  It was written by Mark Wilding and directed by Tony Phelan.  The episode was originally broadcast on the American Broadcasting Company (ABC) in the United States on October 15, 2009.  In the episode, the physicians of Seattle Grace Hospital must learn to co-operate with new Mercy West residents, who do not act in a kind manner to them.  Other storylines include Dr. Callie Torres (Sara Ramirez)'s father returning to the hospital to condemn her homosexuality, and Dr. Izzie Stevens (Katherine Heigl) putting her career into jeopardy after administering the wrong treatment to a patient.

Supporting paragraphs: Mother's Mercy Game of Thrones (season 5)
Answer: 50th