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
import sys
numbers = [int(i) for i in sys.stdin.readline().split() ]
k = numbers[0]
n = numbers[1]
w = numbers [2]
total_price = 0
i=1
while i <= w:
  total_price += i*k
  i+=1
if n>= total_price:
  print("0")
else:
  print (total_price - n)     

