# CF546A Soldier and Bananas

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• 735提交
• 题目来源
• 评测方式 RemoteJudge
• 标签 字符串 数论,数学 概率论,统计
• 难度 入门难度
• 时空限制 1000ms / 256MB
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## 题意翻译

一个士兵想在商店里买W个香蕉。他必须为第一个香蕉支付K美元，第n个香蕉需要K*n美元

他有N元。他从他的朋友士兵那里借了多少美元去买W香蕉？

感谢@something 提供的翻译

## 题目描述

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?

## 输入输出格式

输入格式：

The first line contains three positive integers $k,n,w$ ( $1<=k,w<=1000$ , $0<=n<=10^{9}$ ), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.

输出格式：

Output one integer — the amount of dollars that the soldier must borrow from his friend. If he doesn't have to borrow money, output $0$ .

## 输入输出样例

输入样例#1： 复制
3 17 4

输出样例#1： 复制
13
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