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?

Input

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

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.

Examples

Input

3 17 4


Output

13

k,n,w= raw_input("").split()
k=int(k)
n=int(n)
w=int(w)
borrow = 0
rate = 0
price = 0
total = 0
for i in range(1,w):
	i += 1
	rate=i*k
	price=price+rate
total = k + price
borrow = total - n
if (borrow<0):
	borrow=0
print(borrow)
	



	
	
	
	
	
	
