Soldier and Bananas

题面翻译

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 $0$ .

样例 #1

样例输入 #1

3 17 4

样例输出 #1

13