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
data = raw_input()
data = data.split()
for i in range(0, (len(data)), 1):
    data[i] = long(data[i])

initial_price = data[0]  # intial price of the banana
initial_dollars = data[1]  # initial number of dollars
bananas_wanted = data[2]  # total of bananas wanted
price = 0

price = (initial_price)*(bananas_wanted*(bananas_wanted+1)/2)

lend = price - initial_dollars
if lend > 0:
    print(lend)
else:
    print (0)