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

input =  sys.stdin.readline



def inp():
    return (int(input()))

def inlt():
    return(list(map(int,input().split())))


def insr():
    s = input()
    return(list(s[:len(s) - 1]))



elems = inlt()

k = elems[0]
n = elems[1]
w = elems[2]

i = 1

totPrice = 0


for counter in range(1,w+1):
    totPrice += i*k
    i = i + 1

alfa = totPrice - n

if alfa <= 0:
    print(0)
else:
    print(alfa)


