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
from sys import stdin
def solve(precio,dolar,bananas):
    if bananas==1:
        if precio<=dolar:
            print(0)
        else:
            print(precio-dolar)
    else:
        res=precio*((bananas*(bananas+1))//2)
        if res<=dolar:
            print(0)
        else:
            print(res-dolar)

def main():
    precio,dolar,bananas=m=list(map(int,stdin.readline().strip().split()))
    """precio=int(stdin.readline())
    dolar=int(stdin.readline())
    bananas=int(stdin.readline())"""
    solve(precio,dolar,bananas)

main()
