CodeForces 546 A - Soldier and Bananas

题目链接：click here~~

【题目大意】

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?

【解题思路】

公式：判断(((w+1)*(w)/2)*k-n)是否大于零

代码：

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int k,n,w;
    scanf("%d%d%d",&k,&n,&w);
    printf("%d\n",(((w+1)*(w)/2)*k-n)>0?(((w+1)*(w)/2)*k-n):0);
    return 0;
}