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
# he has n dollars
# i*k dollars for i banan e.g. 10dolalrs for the 10th banana
#  k, n, w (1  ≤  k, w  ≤  1000, 0 ≤ n ≤ 109)

# to get 3 integer inputs:

z = input()
(k, n, w) = list(map(int, z.split()))


x=0
for i in range(w+1):
    x += k*i
# print(x)

# 3 *1, 3*2, 3*3, 3*4 = 3 + 15 +12
result = int(x - n)
if n > x:
    print(0)
else:
    print(result)
