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
# -*- coding: utf-8 -*-
"""
Created on Wed Jul 29 20:40:47 2020

@author: pc
"""

# -*- coding: utf-8 -*-
"""
Created on Wed Jul 29 19:54:13 2020

@author: pc
site : https://codeforces.com/problemset/problem/546/A
"""

import sys
input = sys.stdin.readline

############ ---- Input Functions ---- ############
def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    s = input()
    return(list(s[:len(s) - 1]))
def invr():
    return(map(int,input().split()))

#counting occurence from list
def countX(lst, x): 
    count = 0
    for ele in lst: 
        if (ele == x): 
            count = count + 1
    return count 
    

"""
a, b, c, d = [int(x) for x in input().split()]
print(a*b*c*d)


1) inp — For taking integer inputs.

2) inlt — For taking List inputs.

3) insr — For taking string inputs. Actually it returns a List of Characters, instead of a string, which is easier to use in Python, because in Python, Strings are Immutable.

4) invr — For taking space seperated integer variable inputs.
    
"""

r = inlt()
 
k = r[0]
n=r[1]
w=r[2]

bill = 0
while w !=0 :
    bill = bill + k*w
    w = w-1
    
if bill <= n :
    print(0)
else:
    print(abs(n-bill))
    

min=0
temp=0
s=''