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 sys

local_launch = False
try:
    open('LOCAL').read()
    local_launch = True
except:
    pass
input_data = open('INPUT.txt').read() if local_launch else sys.stdin.read()
done = {'i': 0}
tokens = input_data.split()

def next_token():
    result = tokens[done['i']]
    done['i'] += 1
    return result

def next_int():
    return int(next_token())

def next_str():
    return next_token()

############## BEGIN OF CODE #####################

k = next_int()
n = next_int()
w = next_int()
a = 1
i = 1
while i != w:
    i = i + 1
    a=a+i
u = a * k
if n - u < 0:
    print(u - n)
else:
    print(0)

