1 /*
2 水题：ans = (1+2+3+...+n) * k - n，开long long
3 */
4 #include <cstdio>
5 #include <algorithm>
6 #include <cstring>
7 #include <cmath>
8 using namespace std;
9
10 typedef long long ll;
11
12 int main(void) //Codeforces Round #304 (Div. 2) A. Soldier and Bananas
13 {
14 int k, n, w;
15 while (scanf ("%d%d%d", &k, &n, &w) == 3)
16 {
17 ll sum = (1 + w) * w / 2 * k;
18 if (sum < n) puts ("0");
19 else printf ("%I64d
", sum - n);
20 }
21
22 return 0;
23 }
24
25
26 /*
27 3 17 4
28 */