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
from sys import stdin, stdout

def trace(f):
    def traced(*args, **kw):
        print("calling {} with args {}, {}".format(f.__name__, args, kw))
        return f(*args, **kw)
    return traced

@trace
def f(x):
    print(x)

def read():
    return stdin.readline()[:-1]

def readarr(sep=None, maxsplit=-1):
    return read().split(sep, maxsplit)

def readint():
    return int(read())

def readintarr(sep=None, maxsplit=-1):
    return [int(a) for a in readarr(sep, maxsplit)]

def write(*args, **kwargs):
    sep = kwargs.get('sep', ' ')
    end = kwargs.get('end', '\n')
    stdout.write(sep.join(str(a) for a in args) + end)

def writearr(arr, sep=' ', end='\n'):
    stdout.write(sep.join(str(a) for a in arr) + end)

#writearr([1, 2, 3])
#writearr([1, 2, 3], sep="-", end="!")
#write()
#write(1, 2, 3, sep="-", end="!")


k, actual, bananas = readintarr(" ")
costo = sum(i*k for i in range(1, bananas+1))
#print([i*k for i in range(bananas)])
#print(costo)
faltante = costo - actual
if faltante < 0: faltante = 0
write(faltante)
