A soldier wants to buy *w* bananas in the shop. He has to pay *k* dollars for the first banana, 2*k* 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?
The first line contains three positive integers *k*, *n*, *w* (1  ≤  *k*, *w*  ≤  1000, 0 ≤ *n* ≤ 10<sup class="upper-index">9</sup>), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.
result = ""
s = input().split(" ")
k = int(s[0])
n = int(s[1])
w = int(s[2])
amountToBorrow = 0
if 1 <= k and w <= 1000 and 0 <= n and n <= 10**9:
    dollars = 0
    for i in range(w):
        i += 1
        dollars += i*k
    result = abs(n - dollars)

print(f"{result}")