The last problem had said that bro.kun was wealthy.So this problem we pass through last summer vacation.team ACM want to assemble for training,therefore we had stayed at univercity(some students of 15 grade).One day,bro.kun invite us to buy watermelen juice on our way of domitory after training.There's no way that bro.kun is very enthusiastic,so we agree it.Because of our generous,bro.kun decide to treat us.but he maybe don't have enough cash,but his alipay have infinite money.So bro.kun want to test your ability for code.please help bro.kun to count how much does bro.kun have to pay in alipay.

the first line input three integer N、M、S represent how many classmates does bro.kun treat,how much does a cup of watermelen,and how much cash does bro.kun have to pay for alipay(0<N<50,0<M<20,0<S<=500).

an integer that how much does bro.kun need to pay in alipay.