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
# Problem 546A

def test():
	k, n, w = map(int, input().split())

	total_cost = 0
	#  total_cost for w bananas
	for i in range(1,w+1):
		total_cost += (i)*k
		#print(("%s: %s")%(i, total_cost))

	x = max(0,total_cost-n)

	print(x)
	return x

test()
# w bananas
# n initial number of dollars
# k dollars 1st
# 2k dollars 2nd
# ....
# i*k dollars i-th
# budget: n-dollars

#  max k + 2k + 3k + ... + i*k <= w



