In Tay's postal service, each mailbox is labeled with a letter followed by an integer. Given integers numRows and numColumns, output the label for each mailbox, followed by a space. End each row with a newline.

Rows are in alphabetical order. Mailboxes in the first row all start with the letter A$.$

Columns are in ascending order. Mailboxes in the first column all end with the integer $1.$