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
#k = 3 #cost of first banana
#n = 17 #amount of money
#w = 4 #number of banana

#1  #2  #3  #4
#3  #6  #9  #12
#(1+2+3+4) * k
#total = 30
#differences = total - n

# just to get the input
data = input()
data_list = data.split(" ")
k = int(data_list[0])
n = int(data_list[1])
w = int(data_list[2])

counter = 1
total = 0
while counter <= w:
  total = total + counter
  counter = counter + 1
total = total * k
difference = total - n
if difference>0:
  print(difference)
else:
  print("0")