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
# Soldier and Bananas

# Buy W bananas
# First banana cost k, second 2k, third 3k, and so on
# Output result as the amount of money that needs to be borrowed
# First banana cost, money balance, number of bananas wanted

k, n, w = list(map(int, input().split()))
c = 0  # Cost
for i in range(w):
    c += k*(1+i)
if c > n:
    res = c - n
else:
    res = 0
print(res)
