CREATE TABLE table_25535 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original air date" CLOB)

If the original air date is April 1, 2003, what number in the series is this episode?
SELECT "No. in series" FROM table_25535 WHERE "Original air date" = 'April 1, 2003'
SELECT "No. in series" FROM "table_25535" WHERE "Original air date" = 'April 1, 2003'