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: What is the medium of the work "Escola de atenas - vaticano?"? 
Knowledge Triplets: The School of Athens, visual_art.artwork.media, Plaster
The School of Athens, visual_art.artwork.artist, Raphael
The School of Athens, visual_art.artwork.art_subject, Ancient Greece
Escola de atenas - vaticano, common.image.appears_in_topic_gallery, The School of Athens
m.0c3kbq6, visual_art.artwork_location_relationship.artwork, The School of Athens
The School of Athens, visual_art.artwork.art_form, Painting
Escola de atenas - vaticano, common.image.size, m.0ccj2z8
Painting, base.artmetadata.art_form.medium, Paint
View of the Stanza della Segnatura, common.image.appears_in_topic_gallery, The School of Athens
Ancient Greece, visual_art.art_subject.artwork_on_the_subject, The School of Athens
The School of Athens, common.topic.article, m.025sm_b
The School of Athens, visual_art.artwork.art_genre, History painting
Stanze di Raffaello Frescoes, visual_art.art_series.artworks, The School of Athens
The School of Athens, visual_art.artwork.art_form, Fresco
The School of Athens, visual_art.artwork.media, Paint
The School of Athens, common.topic.notable_for, g.125b8yt73
The School of Athens, common.topic.image, \"The School of Athens\" by Raphael
The School of Athens, visual_art.artwork.owners, m.0c3kcln
m.0c3kcln, visual_art.artwork_owner_relationship.artwork, The School of Athens
The School of Athens, visual_art.artwork.locations, m.0c3kbq6
Raphael, visual_art.visual_artist.art_series, Stanze di Raffaello Frescoes
The School of Athens, common.topic.notable_types, Artwork
Stanze di Raffaello Frescoes, visual_art.art_series.artist, Raphael
The School of Athens, common.topic.image, View of the Stanza della Segnatura
The School of Athens, common.topic.image, Escola de atenas - vaticano
The School of Athens, visual_art.artwork.dimensions_meters, m.0j137bz
The School of Athens, visual_art.visual_art_form.artworks, Fresco
Fresco, visual_art.visual_art_form.artworks, The School of Athens
The School of Athens, visual_art.artwork.belongs_to_series, Stanze di Raffaello Frescoes
The School of Athens, base.schemastaging.context_name.pronunciation, g.125_n48td
Escola de atenas - vaticano, common.topic.image, The School of Athens
Artwork, type.type.properties, Date Begun
Raphael, visual_art.visual_artist.art_forms, Painting
The School of Athens, visual_art.artwork.art_form, Painting
The School of Athens, freebase.valuenotation.has_value, Date Begun
Plaster, visual_art.visual_art_medium.artworks, The School of Athens

Answer: Fresco
Painting