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_string = input().split(" ")

k = int(input_string[0]) #Price of first banana
n = int(input_string[1]) #Dollars soldier has
w = int(input_string[2]) #How many banana he wants

# k = 1, n = 2, w = 1

# first banana = 1 x 1
# second banana = 2 x 3
# third banana = 3 x 3
# fourth banana = 4 x 3

total = 0
for i in range(w):
    total = total + (i+1) * k
borrow = total - n
if borrow > 0:
    print(borrow)
else:
    print(0)
