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
a=input()
b=a.split(' ')
b[0]=int(b[0])
b[1]=int(b[1])
b[2]=int(b[2])
f=b[0]
m=b[0]
c=0
while c<b[2]:
    b[0]=b[0]+f
    f=f+m
    c=c+1
b[0]=b[0]-m
if str(b[0]-b[1])[0]=='-':
    print(0)
else:
    print(b[0]-b[1])
