Medicine for a canker sore = 768 yen ($7.92 €5.91)

My son got a canker sore in his mouth. There are 5 spots of focuses. He gets mad about the trouble in his mouth. I went to a drugstore with my son to buy a medicine for the canker sore. Shop pharmacist recommended the following drug. In Japan, only pharmacists can sell first-class OTC drugs. It cost 768 yen ($7.92 €5.91). Unfortunately it was hard for my son to handle that medicine by himself. He could not paste the medicine on the target spot. He needs some practices.