You are given a sentence in Polish. Your job is to translate the Polish sentence into Japanese.

Po raz pierwszy zaczęły powstawać metropolie z ponad 5 milionami mieszkańców w krajach rozwijających się.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
500万人を超える巨大都市が初めて発展途上国に出現したのです