A soldier wants to buy *w* bananas in the shop. He has to pay *k* dollars for the first banana, 2*k* 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?
The first line contains three positive integers *k*, *n*, *w* (1  ≤  *k*, *w*  ≤  1000, 0 ≤ *n* ≤ 10<sup class="upper-index">9</sup>), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.
n,k=input().split()
if k==0:
    print(int(n))
else:
    while int(k)>0:
        if int(int(n)%10)>=int(k):
            print(int(n)-int(k))
            k=0
        else:
            a=int(int(n)/10)
            b=int(n)%10
            c=int(k)-int(b)-1
            if c==0:
                print(int(a))
                k=0
            else:
                n=a; k=c
