546A. Soldier and Bananas

time limit per test1 second
memory limit per test256 megabytes
inputstandard input
outputstandard output

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).

一名士兵想在商店里买香蕉。他必须为第一根香蕉支付k美元，为第二根香蕉支付2k美元，依此类推（换句话说，他必须为第i根香蕉支付i·k美元）。

He has n dollars. How many dollars does he have to borrow from his friend soldier to buy w bananas?

他有n美元。为了买香蕉，他必须向他的朋友士兵借多少美元？

Input

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.

第一行包含三个正整数k， N w (1 ≤ k, w ≤ 1000, 0 ≤ n ≤ 10 $^{9}$ )，第一根香蕉的价格，士兵最初拥有的美元数量和他想要的香蕉数量。

Output

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.

输出一个整数——士兵必须向朋友借的美元金额。如果他不需要借钱，输出0。

Examples

inputCopy

3 17 4

outputCopy

Solution

Code

#include <iostream>
using namespace std;
//
int main(){
    int k = 0;
    int n = 0;
    int w = 0;
    cin >> k >> n >> w;
    int sum = k * ((1 + w)* w / 2);
    if(sum <= n){
        cout << "0" << endl;
    }else{
        cout << sum - n << endl;
    }
}