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
# n=int(input())
# if(n%2==0):
#     print("YES")
# else:
#     print("NO")
# for _ in range(int(input())):
#     n=(input())
#     if(len(n)<=10):
#         print(n)
#     else:
#         print(n[0]+str(len(n)-2)+n[len(n)-1])
# a=0
# for _ in range(int(input())):
#     n=list(map(int,input().split()))
#     count=0
    
#     for i in range(len(n)):
#         if(n[i]==1):
#             count+=1
#         else:
#             count-=1
#     if(count>0):
#         a+=1
# print(a)
# n,m=map(int,input().split())
# a=list(map(int,input().split()))
# count=0
# for i in range(len(a)):
#     if(a[i]>=a[m-1] and a[i]>0):
#         count+=1
# print(count)
# n,m=map(int,input().split())
# # if((n*m)%2!=0):
# print((n*m)//2)
# # else:
# #     print((n*m)//2)\
# x=0
# for _ in range(int(input())):
#     n=input()
#     if(n=="X++" or n=="++X"):
#         x=x+1
#     else:
#         x=x-1
# print(x)
# n = input()
# m = input()
# n = n.lower()
# m = m.lower()
# if n == m:
#     print("0")
# elif n > m:
#     print('1')
# elif n <m:
#     print('-1')
# matrix=[]
# min=[]
# one_line=0
# one_column=0
# for l in range(0,5):
#     m=input().split()
#     for col,ele in enumerate()

# a = list(map(int,input().split('+')))
# a.sort()
# print('+'.join([str(c) for c in a]))
# n=list(input())
# # if(n[0].islower()):
#     n[0]=n[0].upper()
# else:
#     pass
# print("".join(str(x)for x in n))
# n=list(input())
# s=input()
# count=0
# for i in range(1,len(s)):
#     if(s[i]==s[i-1]):
#         count+=1
# print(count)
# v=["A","O","Y","E","U","I","a","i","e","o","u","y"]
# n=list(input())
# x=[]
# for i in range(len(n)):
#     if n[i] not in v:
#         x.append(n[i])
# print("."+".".join(str(y.lower())for y in x))
# a=[]
# b=[]
# c=[]
# for _ in range(int(input())):
#     x,y,z=map(int,input().split())
#     a.append(x)
#     b.append(y)
#     c.append(z)
# print("YES" if sum(a)==sum(b)==sum(c)== 0 else "NO") 
# m = "hello"
# n=input()
# j=0
# flag=0
# for i in range(len(n)):
#     if(n[i]==m[j]):
#         j=j+1
#     if(j==5):
#         flag=1
#         break
# if(flag==1):
#     print("YES")
# else:
#     print("NO")
# a=set(list(input()))
# print("CHAT WITH HER!" if len(set(list(input())))%2==0 else "IGNORE HIM!")
k,n,w=map(int,input().split())
sum=0
a=[]
for i in range(w+1):
    sum+=k*i
print((sum-n) if sum>n else 0)
