A soldier wants to buy *w* bananas in the shop. He has to pay *k* dollars for the first banana, 2*k* 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?
The first line contains three positive integers *k*, *n*, *w* (1  ≤  *k*, *w*  ≤  1000, 0 ≤ *n* ≤ 10<sup class="upper-index">9</sup>), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants.
#include <iostream>
#include <iomanip>

using namespace std;
int main()
{
	int k, n, w, i, t = 0, m = 0;
    cin >> k >> n >> w;
    for (i = 1; i <= w; i++)
    t += (i * k);
	if (t <= n)
	cout << 0 << endl;
	else 
	cout << t - n << endl;
    
    system("pause");
    return 0;
}