#include <bits/stdc++.h>   int main(void) {     int b_cost, money, b_number;     scanf( %d %d %d , &b_cost, &money, &b_number);     int total_cost;     int loan = 0;     total_cost = b_cost;     for (int i = 2; i <= b_number; i++) {       total_cost += i * b_cost;     }     if (money < total_cost) {       loan = total_cost - money;     }     printf( %d , loan);     return 0;   }   