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=map(int,raw_input().split())
new=[]
u=10
h=0
tl=0
for i in range(1, w+1):
		h=h +i*k
		tl=h-n
		if h<n:
			u=0
			tl=u
		
print tl
		#h+=1
		#h+=1
		#new.append(h)
		#for j in range (0, w):
		#	tl=new[0]+new[:j]
#print tl
			
			
			

#print h
