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(' ')
c=[ ]
ab=0
cb=0
for i in b:
   c.append(int(i))
cb=c[2]
for i in range(1, cb+1):
   ab +=i  * c[0]
if(c[1]>=ab):
   print(0)
else:
   print(ab-c[1])
			  	   	 					 	 			    			