user: You are a structured reasoning expert tasked with solving problems step by step. 
You first think about the reasoning process in the mind and then provide the answer. The reasoning process and answer should be enclosed within <think> </think> and <answer> </answer> tags, respectively, i.e., <think> reasoning process here </think> <answer> answer here </answer>. 
Given a question and the associated knowledge graph triplets (entity, relation, entity), you are asked to answer the question with these triplets and your own knowledge. 
You can break down the original question into several sub-questions and explore the given knowledge graph to solve them step-by-step. If there are multiple possible answers, choose one as the final answer. 
After thinking, when you finally reach a conclusion, clearly state the answer within <answer> </answer> tags, i.e., <answer> answer here </answer>. 
Question: when was the printing press invented by gutenberg? 
Knowledge Triplets: Mainz, travel.travel_destination.tourist_attractions, Gutenberg Museum
Johannes Gutenberg, freebase.valuenotation.is_reviewed, Date of death
Printing press, law.invention.date_of_invention, 1440
m.09xsh6z, common.webpage.resource, From Our Staffers: 'Gutenberg! The Musical!'
Inventions, type.property.expected_type, Invention
m.03phhvg, people.place_lived.person, Johannes Gutenberg
Invention, freebase.type_profile.strict_included_types, Non-Agent
Johannes Gutenberg, people.person.education, m.04hdf4c
m.09vj0j7, base.yupgrade.user.topics, Printing press
Invention, type.type.expected_by, Inventions
Johannes Gutenberg, freebase.valuenotation.is_reviewed, Place of death
Technology, common.topic.image, Handtiegelpresse von 1811
Invention, freebase.type_profile.strict_included_types, Topic
Mainz, base.biblioness.bibs_location.country, Germany
Johannes Gutenberg, people.person.profession, Printer
Parents, owl#inverseOf, Children
Printing press, common.topic.notable_for, g.1255pjwdy
Johannes Gutenberg, symbols.name_source.namesakes, Gutenberg Bible
m.09dvt_4, base.ontologies.ontology_instance_mapping.ontology, OpenCyc
Johannes Gutenberg, freebase.valuenotation.has_value, Siblings
Johannes Gutenberg, base.kwebbase.kwtopic.connections_to, aldus manutius used press of johannes gutenberg
Inventions, rdf-schema#range, Invention
Inventions, type.property.master_property, Inventor
From Our Staffers: 'Gutenberg! The Musical!', common.resource.annotations, m.09xsh6z
Newsweek, base.yupgrade.user.topics, Printing press
m.0qstl7s, dataworld.gardening_hint.last_referenced_by, Printing press
Visual Artist, freebase.type_profile.published, Published
Gutenberg Museum, location.location.containedby, Germany
Johannes Gutenberg, base.kwebbase.kwtopic.has_sentences, By the late 1430s he had apparently begun experimenting with printing.
Printing press, law.invention.date_of_invention, 1440
David Cohn, base.yupgrade.user.topics, Printing press
Johannes Gutenberg, base.kwebbase.kwtopic.has_sentences, If this is correct, then he must clearly have discovered a quick and easy method of making type.
Printing press, user.avh.default_domain.ellerdale_topic.ellerdale_id, 009a-28ca
Invention, type.type.properties, Inventor
m.09vj0kh, base.yupgrade.user.topics, Printing press
Invention, freebase.type_profile.kind, Definition
Johannes Gutenberg, freebase.valuenotation.has_no_value, Children
m.075_7m7, base.yupgrade.user.topics, Printing press
Invention, type.type.properties, Patents
Johannes Gutenberg, freebase.valuenotation.has_value, Cause of death
Johannes Gutenberg, common.topic.article, m.0406c
Handtiegelpresse von 1811, common.image.appears_in_topic_gallery, Technology
m.07c_tcj, base.yupgrade.user.topics, Printing press
University of Mainz, education.educational_institution_campus.educational_institution, University of Mainz
Invention, freebase.type_profile.published, Published
Johannes Gutenberg, base.kwebbase.kwtopic.has_sentences, His press was improved by Blaeuw.
Visual Artist, freebase.type_hints.included_types, Topic
Printing press, common.topic.notable_types, Invention
Johannes Gutenberg, base.kwebbase.kwtopic.connections_from, johannes gutenberg invention improved by willem blaeu
Johannes Gutenberg, symbols.name_source.namesakes, Project Gutenberg
Invention, freebase.type_hints.included_types, Topic
Johannes Gutenberg, base.kwebbase.kwtopic.connections_to, willem blaeu improved design of johannes gutenberg
Invention, freebase.type_profile.equivalent_topic, Invention
Johannes Gutenberg, people.person.ethnicity, Germans
Johannes Gutenberg, freebase.valuenotation.has_no_value, Spouse (or domestic partner)
m.06wft1x, base.yupgrade.user.topics, Printing press
Parents, type.property.reverse_property, Children
Handtiegelpresse von 1811, common.image.appears_in_topic_gallery, Printing press
m.04hdf4c, education.education.student, Johannes Gutenberg
Invention, type.type.domain, Law
Johannes Gutenberg, common.topic.notable_types, Visual Artist
Printing press, common.topic.image, Handtiegelpresse von 1811
Johannes Gutenberg, base.kwebbase.kwtopic.has_sentences, Gutenberg was ruined.
Invention, type.type.expected_by, Associated Inventions
Children, type.property.master_property, Parents
Johannes Gutenberg, symbols.name_source.namesakes, Gutenberg Museum
Johannes Gutenberg, base.kwebbase.kwtopic.has_sentences, He died three years later.
Handtiegelpresse von 1811, common.image.size, m.0291dgt
Printing press, common.topic.article, m.05sy2
Wired, base.yupgrade.user.topics, Printing press
University of Mainz, symbols.namesake.named_after, Johannes Gutenberg
Johannes Gutenberg, base.kwebbase.kwtopic.has_sentences, Two years later Fust invested more and became Gutenberg's partner.
m.09dvt_4, base.ontologies.ontology_instance_mapping.freebase_topic, Printing press
Johannes Gutenberg, law.inventor.inventions, Printing press
Johannes Gutenberg, freebase.valuenotation.is_reviewed, Parents
HuffingtonPost.com, base.yupgrade.user.topics, Printing press
m.0b838kr, base.yupgrade.user.topics, Printing press
Johannes Gutenberg, people.person.places_lived, m.03phhvg
Johannes Gutenberg, common.topic.notable_for, g.125h4qyrq
Visual Artist, freebase.type_profile.strict_included_types, Topic
press.noun.03, base.wordnet.synset.equivalent_topic, Printing press
m.09vj0k5, base.yupgrade.user.topics, Printing press
Johannes Gutenberg, symbols.name_source.namesakes, Gutenberg-Gymnasium Erfurt
Johannes Gutenberg, people.person.place_of_birth, Mainz
Johannes Gutenberg, people.person.profession, Engraver
Johannes Gutenberg, common.topic.image, Johannes Gutenberg
Printing press, base.ontologies.ontology_instance.equivalent_instances, m.09dvt_4
Johannes Gutenberg, people.person.gender, Male
m.03phhvg, people.place_lived.location, Mainz
Johannes Gutenberg, base.argumentmaps.innovator.original_ideas, Movable type
m.09xsh6z, common.webpage.in_index, Entertainment Weekly annotation index
Johannes Gutenberg, symbols.name_source.namesakes, Gutenberg
Mainz, location.location.containedby, Germany
University of Mainz, location.location.containedby, Germany
Gutenberg Museum, symbols.namesake.named_after, Johannes Gutenberg
Johannes Gutenberg, base.kwebbase.kwtopic.connections_from, johannes gutenberg invention user was aldus manutius
m.09xsh6z, common.webpage.topic, Printing press
Johannes Gutenberg, people.person.profession, Inventor
University of Mainz, education.educational_institution.campuses, University of Mainz
Johannes Gutenberg, people.person.parents, Else Wyrich
Johannes Gutenberg, people.deceased_person.place_of_death, Mainz
Johannes Gutenberg, freebase.valuenotation.has_value, Height
Invention, type.type.properties, Date of invention
Johannes Gutenberg, people.person.parents, Friele Gensfleisch zur Laden
Invention, common.topic.article, m.0dgm6_m
Mainz, location.location.contains, University of Mainz
Germans, people.ethnicity.geographic_distribution, Germany
Printing press, common.topic.webpage, m.09xsh6z
Johannes Gutenberg, symbols.name_source.namesakes, University of Mainz
University of Mainz, location.location.containedby, Mainz
m.075_7gq, base.yupgrade.user.topics, Printing press
Printing press, law.invention.inventor, Johannes Gutenberg
Johannes Gutenberg, base.kwebbase.kwtopic.has_sentences, Gutenberg changed history with his typeface and printing press.
Johannes Gutenberg, people.person.nationality, Germany
Gutenberg Museum, travel.tourist_attraction.near_travel_destination, Mainz
m.09vj0jw, base.yupgrade.user.topics, Printing press

Answer: 1440