Soldier and Bananas

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

3 17 4

输出样例 #1

13