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?

Input

The first line contains three positive integers k, n, w (1 ≤ k, w ≤ 1000, 0 ≤ n ≤ 109), the cost of the first banana, initial number of dollars the soldier has and number of bananas he wants. 

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.

Examples

Input

3 17 4


Output

13
#include <bits/stdc++.h>
using namespace std;
inline int max2(int a, int b) { return ((a > b) ? a : b); }
inline int min2(int a, int b) { return a < b ? a : b; }
inline int max3(int a, int b, int c) { return max2(a, max2(b, c)); }
long long int gcd(long long int a, long long int b) {
  while (b) {
    long long int temp = a;
    a = b;
    b = temp % b;
  }
  return a;
}
int main() {
  int n, w, k;
  scanf("%d", &k);
  scanf("%d", &n);
  scanf("%d", &w);
  int total = w * (w + 1);
  total = total / 2;
  total = total * k;
  int diff = total - n;
  if (diff > 0)
    printf("%d\n", diff);
  else
    printf("%d\n", 0);
  return 0;
}
