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 = first payment
#n = money owned $
#w = bananas to buy
input_knw = input()

input_knw = input_knw.split(' ')
input_knw = list(map(int, input_knw))

#print(input_knw)

k = input_knw[0]
n = input_knw[1]
w = input_knw[2]
total_payment = 0

for i in range(1,w+1):
    total_payment = total_payment + (i*k)

#print('total payment: ',total_payment)

if total_payment - n > 0:
    print(total_payment - n)
else:
    print(0)
