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
'''w1=input().lower()
w2=input().lower()
sc1=sum([ord(i) for i in w1])
sc2=sum([ord(i) for i in w2])
if sc1>sc2:
    print(1)
elif sc1<sc2:
    print(-1)
else:
    print(0)'''

'''s=input()
if len(s)>1:
    s=s.split('+')
    print('+'.join(sorted(s)))
else:
    print(s)'''

'''s=input()
print(s[0].capitalize()+s[1:])'''

'''n=int(input())
s=input()
ans=0
for i in range(n-1):
    if s[i]==s[i+1]:
        ans+=1
print(ans)'''


'''s=set(input())
if len(s)%2==0:
    print("CHAT WITH HER!")
else:
    print("IGNORE HIM!")'''

'''s=input()
s1=s.find('1111111')
s2=s.find('0000000')
if (s1!=-1 or s2!=-1):
    print('YES')
else:
    print('NO')'''

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

    
