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
'''
delete all the vowels
insert . before each consonant
replace uppercase consonants with lowercase

NOTE:Vowels are letters "A", "O", "Y", "E", "U", "I",
and the rest are consonants

python codeforces.py
'''
'''
vowels=["a", "o", "y", "e", "u", "i"]

string = (input("")).lower()

ans=""
for letter in string:
    if letter not in vowels:
        ans+=("."+letter)

print(ans)
'''
'''
m,n = map(int, input("").split(' '))

if m%2!=0 or n%2!=0:
    print((m*int(n/2))+int(m/2))
else:
    print(m*int(n/2))
'''
'''
if m%2==0:
    print(int(m/2)*n)
elif n%2==0:
    print(int(n/2)*m)
else:
    print((int(m/2)*n)+int(n/2))
'''
'''
n = int(input(""))
x=0
code=[]

for i in range(n):
    code.append(input(""))

for line in code:
    if "++" in line:
        x+=1
    else:
        x-=1

print(x)
'''
'''
string=[]
for i in range(2):
    string.append(input("").lower())

if string[0]<string[1]:
    print(-1)

elif string[0]==string[1]:
    print(0)

else:
    print(1)
'''
'''
positions=input("")

if len(positions)<7:
    print("NO")

else:
    counter=[0,0]
    flag=0
    for i in positions:
        if i=='0':
            if counter[1]!=0:
                counter[1]=0
                counter[0]+=1
            else:
                counter[0]+=1
        elif i=='1':
            if counter[0]!=0:
                counter[0]=0
                counter[1]+=1
            else:
                counter[1]+=1
        #print(counter)

        if (counter[0]>=7 or counter[1]>=7) and flag==0:
            print("YES")
            flag=1

    if flag==0:
        print("NO")
'''
'''
sum_input=input("")
numbers=[]

for i in sum_input:
    if i != '+':
        numbers.append(int(i))

numbers=sorted(numbers)
ans=''
for j in numbers:
    ans=ans+(str(j)+'+')

ans=ans[:-1]

print(ans)
'''
'''
matrix=[]

for i in range(5):
    temp=input("").replace(' ','')
    matrix.append(list(temp))

#print(matrix)

for i in range(5):
    for j in range(5):
        if matrix[i][j]=='1':
            x=j
            y=i

print(abs(2-x)+abs(2-y))
'''
'''
word=input("")

print(word[0].upper()+word[1:])
'''
'''
R for red
G for green
B for blue

Count the minimum number of stones
to take from the table
so that any two neighboring stones
had different colors.
'''
'''
n=int(input(""))
s=input("")

print(sum([1 for i in range(n-1) if s[i]==s[i+1]]))
'''
'''
username = input("")
#odd->male->ignore him
#even->female->chat with her

letters=[]
counter=0

for char in username:
    if char not in letters:
        counter+=1
    letters.append(char)

if counter%2!=0:
    print("IGNORE HIM!")
else:
    print("CHAT WITH HER!")
'''

'''
a->exits
b->enters

n->number of tram's stops
'''
'''
n=int(input(""))

a=[]
b=[]

for j in range(n):
    x,y=map(int,input("").split())
    a.append(x)
    b.append(y)

current=0
m=[]
for i in range(n):
    current=current-a[i]+b[i]
    m.append(current)

print(max(m))
'''
'''
msg=input("")

def char_finder(s,char):
    counter=0
    for i in s:
        if i==char:
            counter+=1
    return counter

def index_finder(s,char):
    if char_finder(s,char)<=1:
        for i in range(len(s)):
            if s[i]==char:
                return i
    else:
        index=[]
        for i in range(len(s)):
            if s[i]==char:
                index.append(i)
        return index

def my_min(x):
    if isinstance(x,list):
        return min(x)
    else:
        return x

def my_max(x):
    if isinstance(x,list):
        return max(x)
    else:
        return x

l=index_finder(msg,'l')
if isinstance(l,int):
    print("NO")

else:
    h=my_min([i for i in range(len(msg)) if msg[i]=='h'])+1
    o=my_max([i for i in range(len(msg)) if msg[i]=='o'])+1

    if o>h:
        flag=False
        s=msg[h:o]

        for i in s:
            if i=='e':
                e=s.find('e')+1
                s1=s[e:]
                for j in s1:
                    if j=='l':
                        l=s1.find('l')+1
                        s2=s1[l:]
                        for k in s2:
                            if k=='l':
                                ll=s2.find('l')+1
                                s3=s2[ll:]
                                if 'o' in s3:
                                    flag=True
        if flag:
            print("YES")
        else:
            print("NO")
'''
'''
n=int(input(""))
student=list(input("").split(" "))
taxi=0
three=[]
two=[]
one=[]
for i in student:
    if i=='4':
        taxi+=1
    elif i=='3':
        three.append(3)
    elif i=='2':
        two.append(2)
    else:
        one.append(1)

if len(three)>len(one):
    taxi+=len(three)
    #we dont need the lists one and three anymore
    if len(two)%2==0:
        taxi+=int(len(two)/2)
    else:
        taxi+=(int(len(two)/2)+1)

elif len(one)>len(three):
    taxi+=len(three)
    #we dont need the list three anymore
    for i in range(len(three)):#???
        one.remove(1)
    if len(one)%2==0:
        for i in range(int(len(one)/2)):
            two.append(2)
        if len(two)%2==0:
            taxi+=int(len(two)/2)
        else:
            taxi+=(int(len(two)/2)+1)
    else:
        # arta kalan 1 var
        for i in range(int(len(one)/2)):
            two.append(2)
            for j in range(2):
                one.remove(1)
        if len(two)%2==0:
            taxi+=int((len(two)/2)+len(one))
        else:
            taxi+=(int(len(two)/2)+1)

else:
    taxi+=len(one)
    #one ve three ile işim kalmadı
    if len(two)%2==0:
        taxi+=int(len(two)/2)
    else:
        taxi+=(int(len(two)/2)+1)

print(taxi)
'''
k,n,w=map(int,input("").split(" "))
cost=0
for i in range(1,w+1):
    cost+=(k*i)
if cost>n:
    print(cost-n)
else:
    print(0)













