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.
# la complejidad es O(k), ya que el ciclo "while i<=k:" se repite hasta que i sea igual que k(la cantidad de platanos)
k, n, w=map(int,input().split())
#k costo primer platano
#n cant inicial dolares
#w cant platanos que quiere
i = 0 
v=0
vt=0 
r=0 
while i<=k:
    v=k*i
    vt=vt+v
    i +=1

r= vt-n
if vt>n:
    print(0)
else:
    print(r)
	   			 	  		     							  	 		