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

# # A. Soldier and Bananas
# 
# 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.

# w> banans 
# 1k > first 
# 2k > second 
# 3k > third ....
# 

# In[7]:


k,n,w=map(int,input().split())
sum=0
for i in range(1,w+1):
    sum=sum+i*k
if sum<n:
    print(0)
else : 
    print(sum-n)
    


# In[ ]:




