CREATE TABLE table_203_413 (id NUMBER, "rank" CLOB, "city" CLOB, "population" NUMBER, "area\ ( km2 ) " NUMBER, "density\ ( inhabitants/km2 ) " NUMBER, "altitude\ ( mslm ) " NUMBER)

what is the difference between the population of ovada and the population of serravalle scrivia ?
SELECT (SELECT "population" FROM table_203_413 WHERE "city" = 'ovada') - (SELECT "population" FROM table_203_413 WHERE "city" = 'serravalle scrivia')
SELECT (SELECT "population" FROM "table_203_413" WHERE "city" = 'ovada') - (SELECT "population" FROM "table_203_413" WHERE "city" = 'serravalle scrivia')