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: mr.math - Hakimov Rahimjon     |
|    e-mail: mr.math0777@gmail.com          |
"""""""""""""""""""""""""""""""""""""""""""""
#inp = open("lepus.in", "r"); input = inp.readline; out = open("lepus.out", "w"); print = out.write
TN = 1


# ===========================================
  
  
def solution():
    k, n, w = map(int, input().split())
    od = (k+w*k)*w//2-n
    if od>0: print(od)
    else: print(0)


# ===========================================
while TN != 0:
    solution()
    TN -= 1
# ===========================================
#inp.close()
#out.close()