#include <bits/stdc++.h>   using namespace std;   int main() {     int k, n, w, q, cem = 0;     cin >> k >> n >> w;     for (int i = 1; i <= w; i++) {       cem = cem + i * k;     }     if (n <= cem) {       cout << cem - n;     } else       cout << 0;     return 0;   }   