A. Soldier and Bananas

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

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.

Sample test(s)

input

3 17 4

output

13

解题说明：此题是一道数学题，计算前几个找到计算公式就能够进行求解。

#include <stdio.h>

int main()
{
int k,n,w;
int temp;
scanf("%d%d%d",&k,&n,&w);
temp=(w*(w+1)*k)/2-n;
if(temp<0)
{
temp=0;
}
printf("%d\n",temp);
return 0;
}