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
def seperateints(x):
    k=''
    l=[]
    for i in x :
        if i==' ' :
            l.append(int(k))
            k=''
            continue 
        k=k+i
    l.append(int(k))   
    return(l)
l=seperateints(input())
n=0
for i in range(1,l[2]+1) :
    n=n+i*l[0]
if n >l[1] :
     print(n-l[1])
else : print(0)     