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.
k, initial_money, banana_number = map(
    int, input().split())  # k=the cost of the first banana
sum = 0
for i in range(banana_number):
    i = i+1
    sum = sum+i
total_money = k*(sum)
borrowed_money = int(total_money-initial_money)
print(borrowed_money)
if (initial_money >= total_money):
    print("0")
