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
# tested by Hightail - https://github.com/dj3500/hightail
from __future__ import division, print_function
import itertools as it
import sys


def main():
    """Main."""
    k, n, w = read_int_array()
    write(max(0, k * w * (w + 1) // 2 - n))


def bye(message=None):
    if message is not None:
        write(message)
    sys.exit()


def read(func=None):
    a = sys.stdin.readline().rstrip('\n')
    return a if func is None else func(a)


def read_array(func=None, sep=None, maxsplit=-1):
    array = read().split(sep, maxsplit) if sep != '' else list(read())
    return array if func is None else [func(a) for a in array]


def read_2d_array(n, func=None, sep=None, maxsplit=-1):
    return [read_array(func, sep, maxsplit) for _ in it.repeat(None, n)]


def read_int():
    return read(int)


def read_int_array(sep=None, maxsplit=-1):
    return read_array(int, sep, maxsplit)


def read_int_2d_array(n, sep=None, maxsplit=-1):
    return [read_array(int, sep, maxsplit) for _ in it.repeat(None, n)]


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


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


def write_2d_array(array, **kwargs):
    [write_array(a, **kwargs) for a in array]


def _main_():
    name = ''
    names = ''
    if name or names:
        in_name = name + '.in' if name else 'input.txt'
        out_name = name + '.out' if name else 'output.txt'
        stdin = sys.stdin
        stdout = sys.stdout
        sys.stdin = open(in_name)
        sys.stdout = open(out_name, 'w')
        main()
        sys.stdin.close()
        sys.stdout.close()
        sys.stdin = stdin
        sys.stdout = stdout
    else:
        main()


_main_()
