A_Bear_and_Big_Brother.cpp

#include <bits/stdc++.h>
using namespace std;
 
int main() {
    int a;
    int b;
    int c;
    cin>>a>>b>>c;
    int oi=0;
    int pre=0;
    while(oi<c){
        oi=oi+1;
        pre=pre+(a*oi);
    }
    if (pre<=b){
        cout<<0;
    }
    else{
        pre=abs(pre-b);
        cout<<pre;
    }
}