Instructions: You are given a paragraph, with numbered sentences, and a question. Write the numbers of the sentences needed to answer the given question. Separate multiple sentence numbers with a comma (", "). E.g. "1, 2" would be the correct response if Sent 1 and Sent 2 are needed to answer the given question (do not include sentences that contain no information that is necessary to answer the question). Sort the sentence numbers in an increasing order (i.e., '1, 2', instead of '2, 1'). Your answer should not contain anything than the sentence numbers separated by a comma (e.g. '1, 2, 3, 4'). The given question requires more than one sentence to answer. So, your answer must contain at least one comma (", ").
Input: Paragraph- Sent 1: Einstein visited New York City for the first time on 2 April 1921, where he received an official welcome by Mayor John Francis Hylan, followed by three weeks of lectures and receptions.
Sent 2: He went on to deliver several lectures at Columbia University and Princeton University, and in Washington he accompanied representatives of the National Academy of Science on a visit to the White House.
Sent 3: On his return to Europe he was the guest of the British statesman and philosopher Viscount Haldane in London, where he met several renowned scientific, intellectual and political figures, and delivered a lecture at King's College.
Sent 4: He also published an essay, "My First Impression of the U.S.A.," in July 1921, in which he tried briefly to describe some characteristics of Americans, much as Alexis de Tocqueville did, who published his own impressions in Democracy in America (1835).
Sent 5: For some of his observations, Einstein was clearly surprised: "What strikes a visitor is the joyous, positive attitude to life .
Sent 6: The American is friendly, self-confident, optimistic, and without envy."Sent 7: In 1922, his travels took him to Asia and later to Palestine, as part of a six-month excursion and speaking tour, as he visited Singapore, Ceylon and Japan, where he gave a series of lectures to thousands of Japanese.
Sent 8: After his first public lecture, he met the emperor and empress at the Imperial Palace, where thousands came to watch.
Sent 9: In a letter to his sons, Einstein described his impression of the Japanese as being modest, intelligent, considerate, and having a true feel for art.
Sent 10: On his return voyage, he visited Palestine for 12 days in what would become his only visit to that region.
Sent 11: Einstein was greeted as if he were a head of state, rather than a physicist, which included a cannon salute upon arriving at the home of the British high commissioner, Sir Herbert Samuel.
Sent 12: During one reception, the building was stormed by people who wanted to see and hear him.
Sent 13: In Einstein's talk to the audience, he expressed happiness that the Jewish people were beginning to be recognized as a force in the world. 
Question: What did Einstein initially think about Americans?.
Output:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
5, 6.