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
inp = str(input())
inplist = inp.split()
k = int(inplist[0])#cost
n = int(inplist[1])#penny
w = int(inplist[2])#want

if (k >= 1 ):
    if (w <= 1000 ):
        if(n >=0 and n <= 10**9):
            total = 0
            for i in range(w):
	            x = (i + 1 ) * k
	            total += x
            utang = total - n
            if (utang <= 0):
                print(0)
            else:
                print(utang)
        else:
            exit(0)
    else:
        exit(0)
else:
    exit(0)