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
zeile1 = input("")

l = []
zahl = ""

for i in range(len(zeile1)):
	if (zeile1[i] != " "):
		zahl = zahl + zeile1[i]
	else:
		l.append(int(zahl))
		zahl = ""
		
	if (i == (len(zeile1)-1)):
		l.append(int(zahl))
		zahl = ""

summe = 0
k = l[0]
n = l[1]
w = l[2]

for i in range(w):
    summe += (k * (1 + i))

summe -= n

if (summe >= 0):
    print(summe)
else:
    print(0)