Soldier and Bananas

题意翻译

有个士兵想买 $w$ 个香蕉,第 $i$ 个香蕉需支付 $ki$ 元。 现在他手里有 $n$ 元,问他至少要借多少钱才能买到 $w$ 个香蕉?(不需要借钱输出 $0$)。 输入一行三个整数 $n$, $k$, $w$, 含义如题面。

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