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·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≤k,w≤1000, 0≤n≤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.
3 17 4
13