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,n,w=input().split()
# k : dollar for 1 banana
# n : amout
# w : number of banana wanna buy
k1=int(k)
n1= int(n)
w1= int(w)
amount=0

for i in range (1,w1+1):
  # print (i)
  amount = amount + i*int(k1)
  # print (amount)
borrow=0
if n1<amount:
  borrow= amount - n1

print(borrow)