How many papers were written by authors who cooperated with University of Hong Kong?
University of Hong Kong' is an affiliation
SELECT COUNT(T2.PaperId) FROM Author AS T1 INNER JOIN PaperAuthor AS T2 ON T1.Id = T2.AuthorId WHERE T1.Affiliation = 'University of Hong Kong'
CREATE TABLE IF NOT EXISTS "Author"
(
    Id          INTEGER
        constraint Author_pk
            primary key,
    Name        TEXT,
    Affiliation TEXT
);
CREATE TABLE IF NOT EXISTS "Conference"
(
    Id        INTEGER
        constraint Conference_pk
            primary key,
    ShortName TEXT,
    FullName  TEXT,
    HomePage  TEXT
);
CREATE TABLE IF NOT EXISTS "Journal"
(
    Id        INTEGER
        constraint Journal_pk
            primary key,
    ShortName TEXT,
    FullName  TEXT,
    HomePage  TEXT
);
CREATE TABLE Paper
(
    Id           INTEGER
            primary key,
    Title        TEXT,
    Year         INTEGER,
    ConferenceId INTEGER,
    JournalId    INTEGER,
    Keyword      TEXT,
    foreign key (ConferenceId) references Conference(Id),
    foreign key (JournalId) references Journal(Id)
);
CREATE TABLE PaperAuthor
(
    PaperId     INTEGER,
    AuthorId    INTEGER,
    Name        TEXT,
    Affiliation TEXT,
    foreign key (PaperId) references Paper(Id),
    foreign key (AuthorId) references Author(Id)
);
