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
# k banana price  
# n dollars he has
# w amount of bananas 

def string_list_to_int(string_list):

	int_list = []

	for i in range(0,len(string_list)):

		int_list.append(int(string_list[i]))

	return int_list

banana_data = input()


line = banana_data.split()


line = string_list_to_int(line)

banana_price = line[0]
soldier_dollars = line[1]
amount_of_bananas = line[2]

over_all_banana_price = 0

for i in range(0,amount_of_bananas+1):

	banana_dollar_price = banana_price * i

	over_all_banana_price = over_all_banana_price + banana_dollar_price

if soldier_dollars < over_all_banana_price:
	result = over_all_banana_price - soldier_dollars

else:
	result = 0

print(result)




