You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule N-[(3R,8R,9aS)-3-[(4-hydroxyphenyl)methyl]-1,4-dioxo-3,6,7,8,9,9a-hexahydro-2H-pyrido[1,2-a]pyrazin-8-yl]furan-2-carboxamide .
user
C20H21N3O5
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