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
data=input("")
#for determining k
space1_pos=data.find(' ')
#print(space1_pos)
k=int(data[:space1_pos])
#print(k)

#for determining n
data_2=data[space1_pos+1:]
#print(data_2)
space2_pos=data_2.find(' ')
n=int(data_2[:space2_pos])
#print(n)

#for determining w
w=int(data_2[space2_pos+1:])
#print(w)

i=1
cost=0
while i<=w:
    cost=cost+i*k
    i=i+1

borrow=cost-n
if borrow<=0:
    print('0')
else:
    print(borrow)
#print(borrow)
