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
data = input()

l = []
t = ""
for i in data:
	if i == " ":
		l.append(t)
		t = ''
	else:
		t += i
l.append(t)
k = l[0]
n = l[1]
w = l[2]
banana = 0
# print(l)

for i in range(int(w)+1):
	# print(i)
	banana += int(k) * i
	# print(banana)

if banana <= int(n):
	print(0)
else:
	print(banana - int(n))
