Given the task definition, example input & output, solve the new input case.
Answer the question from the given passage. Your answer should be directly extracted from the passage, and it should be a single entity, name, or number, not a sentence.
Example: Passage: Martin Luther married Katharina von Bora, one of 12 nuns he had helped escape from the Nimbschen Cistercian convent in April 1523, when he arranged for them to be smuggled out in herring barrels. Suddenly, and while I was occupied with far different thoughts, he wrote to Wenceslaus Link, “the Lord has plunged me into marriage. At the time of their marriage, Katharina was 26 years old and Luther was 41 years old. Question: In a letter who did Luther credit for his union with Katharina?
Output: the Lord
The paragraph clearly states that, Luther has credited the Lord for his union with Katharina, hence the Lord is correct answer.

New input case for you: Passage: The principal Treaties that form the European Union began with common rules for coal and steel, and then atomic energy, but more complete and formal institutions were established through the Treaty of Rome 1957 and the Maastricht Treaty 1992 (now: TFEU). Minor amendments were made during the 1960s and 1970s. Major amending treaties were signed to complete the development of a single, internal market in the Single European Act 1986, to further the development of a more social Europe in the Treaty of Amsterdam 1997, and to make minor amendments to the relative power of member states in the EU institutions in the Treaty of Nice 2001 and the Treaty of Lisbon 2007. Since its establishment, more member states have joined through a series of accession treaties, from the UK, Ireland, Denmark and Norway in 1972 (though Norway did not end up joining), Greece in 1979, Spain and Portugal 1985, Austria, Finland, Norway and Sweden in 1994 (though again Norway failed to join, because of lack of support in the referendum), the Czech Republic, Cyprus, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia in 2004, Romania and Bulgaria in 2007 and Croatia in 2013. Greenland signed a Treaty in 1985 giving it a special status. Question: When did Denmark join the EU?
Output:
1972