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
#include<stdio.h> int main() { int k,n,w,sum=0,i=1; scanf("%d%d%d",&k,&n,&w); while(w--) { sum+=i*k; i++; } sum<n?printf("0\n"):printf("%d\n",sum-n); }