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
'''
The first value stands for the cost of the first banana;
The second one is initial number of dollars;
And the last value means number of bananas the soldier wants.
'''

intp = list(input().split(' ')) # input values

first_cost = int(intp[0]) # the cost of the first banana
dol_num = int(intp[1]) # the number of dollars the soldier has
nec_bans = int(intp[-1]) # the number of necessary bananas
req_dol = 0 # final quantity

for i in range(nec_bans):
    req_dol += (i+1) * first_cost

if dol_num > req_dol:
    print(0)
else:
    req_dol -= dol_num
    print(req_dol)
