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.
unos = input()

k,n,w = unos.split(" ")

k = int(k)
n = int(n)
w = int(w)

## k -> cijena prve banane
## n -> koliko novaca ratnik ima 
## w -> broj banan koji hoce

# 3+ 2*3 + 3*3+ 4*3 

# 3+6+9+12 = 30
ukupnaCijena = 3
iter = 1
cijena = 0
while iter<w+1:
    cijena+=k*iter
    iter+=1

missing_money = n-cijena

print(abs(missing_money))