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


【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;
}