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
# print("__L24__")

# A. Мишка и игра

# n = int(input())
#
# MishkaScore, ChrisScore = 0, 0
# MishkaWins, ChrisWins = 0, 0
#
# for i in range(n):
#     MishkaScore, ChrisScore = map(int, input().split())
#     if MishkaScore > ChrisScore:
#         MishkaWins += 1
#     elif ChrisScore > MishkaScore:
#         ChrisWins += 1
#     else:
#         continue
# if MishkaWins > ChrisWins:
#     print("Mishka")
# elif ChrisWins > MishkaWins:
#     print("Chris")
# else:
#     print("Friendship is magic!^^")

# A. Bit++

# n = int(input())
# x = 0
#
# for i in range(n):
#     operation = input()
#     if operation == "X++" or operation == "++X":
#         x += 1
#     elif operation == "X--" or operation == "--X":
#         x -= 1
#
# print(x)

# A. Трамвай

# n = int(input())
#
# current_ppl_amount = 0
# tram_max_capacity = 0
#
# for i in range(n):
#     a, b = map(int, input().split())
#     current_ppl_amount -= a
#     current_ppl_amount += b
#     if current_ppl_amount > tram_max_capacity:
#         tram_max_capacity = current_ppl_amount
# print(tram_max_capacity)

# A. Юра и заселение

# n = int(input())
# amount = 0
#
# for i in range(n):
#     p, q = map(int, input().split())
#     if q - p >= 2:
#         amount += 1
# print(amount)

# A. Солдат и бананы

k, n, w = map(int, input().split())
total_price = 0

for i in range(1, w + 1):
    total_price = total_price + (i * k)

if total_price <= n:
    print(0)
else:
    print(total_price - n)

