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
#the cost of the first banana; initial number of dollars;number of bananas he wants
#This program has to print the amount of dollars that the soldier needs to borrow to get the number of banana he wants

#get 3 inputs
k,n,w=list(map(int,input().split()))

totalamountneeded=0
#calculating the total amount of dollars needed to buy w bananas
for i in range(1,w+1):
    
    totalamountneeded=totalamountneeded+(i*k)
#if the current money is equal or bigger than the needed amount, print zero
if(totalamountneeded<=n):
    print(0)
#if the current money is smaller than the needed money, the difference between the totalamount and the current money is additional money he will need to borrow more 
else:
    print(totalamountneeded-n)

#when there are 2 different integers and we are trying to make the smaller one
#equal to the bigger one, the additonal quantity(number) needed for the small
#integer to be equal to the bigger one is equal to the (bigger one minus the smaller one)

#For example 2 integers, 1 and 2. In order for to be equal to be 2, 1 is needed and this 1 is the result of 2-1 which is 1



    
    



