My child stayed in Korea for a short time on an F-1 visa during vacation. As it was a short period, my child did not register as a foreigner. And he or she plan to go back to Uzbekistan on September 1st, but his or her visa will expire on August 25th. The difference is only 7 days. Does he/she needs to extend the visa? If he/she doesn't extend it, will it be a problem the next time he/she enters the country?