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
k, n, w = input().split()
w = int(w)
# for i in range(w):
#     k = int(k)
#     n = int(n)
#     result=1/2*w*(w+1)*k
#     if result>n:
#         print(result-n)
#     else:
#         print(0)
result=0
mylist=[]
for i in range(1,w+1):
    k=int(k)
    n=int(n)
    result=k*i
    mylist.append(result)
    d=sum(mylist)

if d >n:
    print(d-n)
else:
    print(0)
