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
import math,string,itertools,fractions,heapq,collections,re,array,bisect,copy
from itertools import chain, dropwhile, permutations, combinations
from collections import defaultdict, deque

# Guide:
#   1. construct complex data types while reading (e.g. graph adj list)
#   2. avoid any non-necessary time/memory usage
#   3. avoid templates and write more from scratch
#   4. switch to "flat" implementations

def VI(): return list(map(int,input().split()))
def I(): return int(input())
def LIST(n,m=None): return [0]*n if m is None else [[0]*m for i in range(n)]
def ELIST(n): return [[] for i in range(n)]
def MI(n=None,m=None): # input matrix of integers
    if n is None: n,m = VI()
    arr = LIST(n)
    for i in range(n): arr[i] = VI()
    return arr
def MS(n=None,m=None): # input matrix of strings
    if n is None: n,m = VI()
    arr = LIST(n)
    for i in range(n): arr[i] = input()
    return arr
def MIT(n=None,m=None): # input transposed matrix/array of integers
    if n is None: n,m = VI()
    a = MI(n,m)
    arr = LIST(m,n)
    for i,l in enumerate(a):
        for j,x in enumerate(l):
            arr[j][i] = x
    return arr


def run(k,n,w):
    x = 0
    for i in range(1,w+1):
        x += k*i
    if x<=n:
        print(0)
    else:
        print(x-n)

def main(info=0):
    k,n,w = VI()

    run(k,n,w)


if __name__ == "__main__":
    main()
