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
class solution:
    def __init__(self):
        self.list1 = []
        self.rem = 0
        self.w = 0
        self.k = 0
        self.n = 0
        
    def compute(self):
        sum1 = (self.w*(self.w+1))/2
        amount = self.k*sum1
        self.rem = amount - self.n
    
    def change(self):
        self.k = int(self.list1[0])
        self.n = int(self.list1[1])
        self.w = int(self.list1[2])

    def get_input(self):
        str1 = input()
        temp = str1.split()
        self.list1 = temp
        del temp
    
    def check(self):
        if self.rem <= 0:
            self.rem = 0

    def show(self):
        print(int(self.rem))
        
    def execute(self):
        self.get_input()
        self.change()
        self.compute()
        self.check()
        self.show()
    
def main():
    s1 = solution()
    s1.execute()
    
if __name__ == '__main__':
    main()  
    