Untitled

#include <iostream>
using namespace std;

int main()
{
	int k, n, w;
	int sum = 0;
	cin >> k >> n >> w;

	for (int i = 1; i <= w; i++) {
		sum += i * k;
	}
	if (sum > n) {
		cout << sum - n;
	}
	else {
		cout << 0;
	}
}