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
# __author__ = ["Justin Castillo", "Kristian Radam", "Patrick Ragasa", "Marius Sanchez"]

# k - cost of first banana
# n - initial number of dollars
# w - number of bananas
def bananas(k, n, w):
	cost = computeCost(k, w)
	toBorrow = n - cost

	if (toBorrow >= 0):
		return 0
	elif (toBorrow < 0):
		return abs(toBorrow)


def computeCost(init_cost, quantity):
	totalCost = 0
	multiplier = 1

	while (quantity != 0):
		totalCost += multiplier * init_cost
		multiplier += 1
		quantity -= 1

	return totalCost


inputList = raw_input().split()

k = int(inputList[0])
assert(k >= 1)

n = int(inputList[1])
assert(n >= 0 & n <= pow(10, 9))

w = int(inputList[2])
assert(w <= 1000)


print bananas(k, n, w)