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
"""n = int(input())
count = 0
for i in range(n):
	c = 0
	p = [int(k) for k in input().split()]
	for j in p:
		if j == 1:
			c+=1
	if c >=2:
		count+=1
print(count)"""
"""n,k = input().split()
count = 0
scores = [int(i) for i in input().split()]
kth = scores[int(k)-1]
for j in scores:
	if j == 0:
		continue
	elif j>=kth:
		count += 1
print(count)"""
"""word = input()
vowel = ['a','e','i','o','u','y','A','E','I','O','U','Y']
for i in word:
	if i in vowel:
		continue
	elif i not in vowel:
		print('.'+i.lower(),end = '')"""
"""import math
m,n = input().split()
print(math.floor((int(m)*int(n))/2))"""
"""n = int(input())
x = 0
for i in range(n):
	lis = []
	lis = input()
	if (lis[0] == '+'and lis[1]=='+') or (lis[1] == '+' and lis[2] == '+'):
		x += 1
	elif (lis[0] == '-'and lis[1]=='-') or (lis[1] == '-' and lis[2] == '-'):
		x -= 1
print(x)"""
"""s = input()
a = s[0].capitalize()
print(a+s[1:])"""
"""Petya and strings
n1 = input()
n2 = input()
c = 0
for i in range(len(n1)):
	if ord(n1[i].lower()) > ord(n2[i].lower()):
		print(1)
		c = 1
		break
	elif ord(n1[i].lower()) < ord(n2[i].lower()):
		print(-1)
		c = 1
		break
	else:
		continue
if c == 0:
	print(0)"""
"""beautiful matrix
for i in range(5):
	a =[]
	for j in input().split():
		a.append(int(j))
	if 1 in a:
		print(abs(a.index(1)-2)+abs(i-2))"""
"""helpful maths
n = [int(i) for i in input().split('+')]
n.sort()
for i in range(len(n)):
	if i != len(n)-1:
		print(n[i],end='+')
	else:
		print(n[i])"""
"""football
n = input()
if '0000000' in n:
	print('YES')
elif '1111111' in n:
	print("YES")
else:
	print('NO')"""
"""stones on the table
n = int(input())
rock = input()
c = 0
for i in range(n-1):
	if rock[i] == rock[i+1]:
		c += 1
print(c)"""
"""boy or girl
n = input()
c = 0
for i in range(len(n)):
	if i == 0:
		c+=1
	elif n[i] not in n[:i]:
		c+=1
if c%2 == 0:
	print("CHAT WITH HER!")
else:
	print("IGNORE HIM!")"""
"""Young physicist
n = int(input())
x1=y1=z1=0
for i in range(n):
	x,y,z=input().split()
	x1=x1+int(x)
	y1=y1+int(y)
	z1=z1+int(z)
if x1==0 and y1==0 and z1==0:
	print("YES")
else:
	print("NO")"""
"""soldier and banana"""
k,n,w=input().split()
money = 0
for i in range(1,int(w)+1):
	money += int(k)*i
if int(n)>=money:
	print('0')
elif int(n)<money:
	print(abs(money-int(n)))





 


