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
#!/usr/bin/env python
# coding: utf-8

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char1=''


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char1= char1+input()


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list1= char1.split(' ')


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list2=[]


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for n in list1:
    list2.append(int(n))


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sum1 = (list2[2]/2) *(2*list2[0] + (list2[2]-1)*list2[0])


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if int(sum1) > list2[1]:
    print(int(sum1)-list2[1])
else:
    print(0)


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