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
#Problem 546A
s = input("")
input_list = s.split(' ')
values = [int(x.strip()) for x in input_list]
orginal_price = values[0]
money_you_have = values[1]
bananas_you_want = values[2]
price_increase = 1
Total_Cost_local = 0
Total_Cost_global = 0
for x in range(bananas_you_want):
    Total_Cost_local = orginal_price * price_increase
    price_increase += 1 
    Total_Cost_global = Total_Cost_global + Total_Cost_local

if Total_Cost_global - money_you_have < 0:
    print("0")
else:
    print(Total_Cost_global - money_you_have)
