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
Copy
3 17 4
Output
Copy
13
by talk:注意,这里i是第i个,就是说如果我想算三个香蕉的钱,我就得加上第一,第二,第三香蕉的钱。
#include<stdio.h> int main() { int k,n,w; while(scanf("%d%d%d",&k,&n,&w)!=EOF) { int sum=0; for(int i=1;i<=w;i++) sum+=i*k; if(sum<=n) printf("0\n"); else printf("%d\n",sum-n); } return 0; }