Input (grade 13): Gray was also interested in postage stamps; on 1 May 1840, the day the Penny Black first went on sale, he purchased several with the intent to save them, thus making him the world's first known stamp collector.
Output (grade 12): Gray was also interested in postage stamps; on 1 May 1840, the day the Penny Black first went on sale, he bought some to keep, thus making him the world's first known stamp collector.