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 
def main():
    k,n,w = [int(i) for i in input().split()]
    f = lambda k,w : k*(w*w+w)/2
    val = max(0,f(k,w)-n)
    sys.stdout.write("%s\n" % int(val))
if __name__ == "__main__":
    ##sys.stdin = open('oddoreven.in','r')
    ##sys.stdout = open('oddoreven.out','w')
    main()
    ##sys.stdin.close()
    ##sys.stdout.close()
