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
def soldier(arr):
    #print(k,n,w)
    k=arr[0]
    n=arr[1]
    w=arr[2]
    cost=[]
    for i in range(1,w+1):
        cost.append(i*k)
        pass
    total=sum(cost)
    br=total-n
    if(br==0 or br<0):
        print(0)
        pass
    else:
        print(br)
        pass
if __name__ == "__main__":
    arr=[int(i) for i in input().split(' ')]
    soldier(arr)