✔ 문제

✔ 해결

class Solution {
  public long solution(int price, int money, int count) {
    long answer = 0, sub_answer = 0;
    
    for(int i = 0; i <= count; i++) {
      sub_answer += (price * i);
    }
    
    if(sub_answer < money) {
      answer = 0;
    }else {
      answer = sub_answer - money;
    }
    
    return answer;
  }
}