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
# Problem: A. Soldier and Bananas
# Contest: Codeforces - Codeforces Round #304 (Div. 2)
# URL: https://codeforces.com/problemset/problem/546/A
# Memory Limit: 256 MB
# Time Limit: 1000 ms
# 
# Powered by CP Editor (https://cpeditor.org)

""" Python 3 compatibility tools. """
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()))
    
line = inlt()
banana_price = line[0]
soldier_dollars = line[1]
bananas_num = line[2]

# total cost
total_cost = 0
for i in range(1, bananas_num + 1):
    total_cost += i * banana_price
    
diff = total_cost - soldier_dollars
if diff < 0:
    diff = 0
print(diff)