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
input_values = raw_input()
input_list = input_values.split(" ")

first_banana_cost = int(input_list[0])
dollars_soldier_has = int(input_list[1])
bananas_to_buy = int(input_list[2])
total_amount_of_dollars_to_spend = 0
for banana_to_buy in range(1, bananas_to_buy + 1):
    total_amount_of_dollars_to_spend += first_banana_cost * banana_to_buy
money_to_borrow = total_amount_of_dollars_to_spend - dollars_soldier_has
if money_to_borrow > 0:
    print money_to_borrow
else:
    print 0