how many samples have unknown countries of origin?
CREATE TABLE resultsdata15 (
    sample_pk number,
    commod text,
    commtype text,
    lab text,
    pestcode text,
    testclass text,
    concen number,
    lod number,
    conunit text,
    confmethod text,
    confmethod2 text,
    annotate text,
    quantitate text,
    mean text,
    extract text,
    determin text
)

CREATE TABLE sampledata15 (
    sample_pk number,
    state text,
    year text,
    month text,
    day text,
    site text,
    commod text,
    source_id text,
    variety text,
    origin text,
    country text,
    disttype text,
    commtype text,
    claim text,
    quantity number,
    growst text,
    packst text,
    distst text
)
SELECT COUNT(*) FROM sampledata15 WHERE origin = "3"
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: how many samples have unknown countries of origin? ### Input: CREATE TABLE resultsdata15 (
    sample_pk number,
    commod text,
    commtype text,
    lab text,
    pestcode text,
    testclass text,
    concen number,
    lod number,
    conunit text,
    confmethod text,
    confmethod2 text,
    annotate text,
    quantitate text,
    mean text,
    extract text,
    determin text
)

CREATE TABLE sampledata15 (
    sample_pk number,
    state text,
    year text,
    month text,
    day text,
    site text,
    commod text,
    source_id text,
    variety text,
    origin text,
    country text,
    disttype text,
    commtype text,
    claim text,
    quantity number,
    growst text,
    packst text,
    distst text
) ### Response: SELECT COUNT(*) FROM sampledata15 WHERE origin = "3"