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


data=input()

def data_check(d):
    flag=d.split(' ')
    val=money_generator(flag[0],flag[2])
    borrow=val-int(flag[1])


    return borrow



def money_generator(price,amount):
    sum=0
    for x in range(1,int(amount)+1):sum+=int(price)*x

    return sum



if __name__=="__main__":
    b=data_check(data)
    if b > 0:print(b)
    else:print(0)

