A soldier wants to buy w bananas in the shop. He has to pay k dollars for the first banana, 2k dollars for the second one and so on (in other words, he has to pay i \cdot k dollars for the i-th banana).

He has n dollars. How many dollars does he have to borrow from his friend soldier to buy w bananas?

The first line contains three positive integers k,n,w (1 \le k,w \le 1000, 0 \le n \le 109), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.

Output one integer - the amount of dollars that the soldier must borrow from his friend. If he doesn't have to borrow money, output 0.