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
"""
Exercise for strings:
print(''.join('.'+x for x in input().lower() if x not in'aeyoui'))


m, n = [int(x) for x in input().split(' ')]
print(m * n // 2)
print(eval('*'.join(input().split()))//2)

Bit++:
a = 0
sentences = int(input())
for i in range(sentences):
    if '++' in input():
        a += 1
    else:
        a -= 1
print(a)
print(sum(44-ord(input()[1])for i in[0]*int(input())))


a = input().lower()
b = input().lower()
for i in range(1):
    if a < b:
        print(-1)
    elif a > b:
        print(1)
    else:
        print(0)

i = input;
a = i().lower();
b = i().lower()
print((a > b) - (a < b))
"""

# a = []
# for i in range(5):
#     a.append(list(map(int, input().split())))
# steps = 0
# if a[2][2] == 1:
#     print(steps)
# for i in range(len(a)):
#     for j in range(len(a)):
#         b = a[i][j] + 1
#         if b == 2:
#             print(steps)

"""
My solution:
a = input()[::2]
a = [''.join(str(x)) for x in sorted([int(x) for x in a])]
a = '+'.join(a)
print(a)

True solution:
print("+".join(sorted(input()[::2])))

My solution equals to the True solution; Yeah!
a = input()
print(a[0].upper() + a[1:])


My solution:
soccers = input()
a = '1111111'
b = '0000000'
if a in soccers or b in soccers:
    print('YES')
else:
    print('NO')

True solution:
s=input();print(["NO","YES"][7*"1"in s or 7*"0"in s])


My solution:
string = set(input())
if len(string) % 2 == 0:
    print("CHAT WITH HER!")
else:
    print("IGNORE HIM!")

True solution:
print(["CHAT WITH HER!","IGNORE HIM!"][len({*input()})%2])
"""

first_banana, pocket, bananas = [int(x) for x in input().split()]
total_price = 0
for i in range(bananas + 1):
    total_price += i * first_banana
loan = pocket - total_price
if loan >=0 :
    loan = 0
print(abs(loan))
