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 re
def gen(nums):
	return (nums[0]*(nums[2]*(nums[2]+1))/2)-nums[1]

def main():
	nums = raw_input().split(" ")
	nums = map(lambda x: int(x),nums)
	# matrix = [raw_input() for t in range(0,nums)]
	ans = gen(nums)
	if(ans>=0):
		print ans
	else:
		print 0

if __name__ == "__main__":
	main()