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
# 546A

__author__ = 'artyom'

# SOLUTION

def main():
  k, n, w = read(3)
  t = 0
  for i in range(1, w + 1):
    t += i * k
  return max(0, t - n)


# HELPERS


def read(mode=2):
  # 0: String
  # 1: List of strings
  # 2: List of integers
  inputs = input().strip()
  if mode == 0: return inputs
  if mode == 1: return inputs.split()
  if mode == 2: return int(inputs)
  if mode == 3: return list(map(int, inputs.split()))


def write(s="\n"):
  if s is None: s = ""
  if isinstance(s, list): s = " ".join(map(str, s))
  s = str(s)
  print(s, end="")


write(main())