[Lv. 1] 부족한 금액 계산하기

class Solution {
    public long solution(int price, int money, int count) {
        long answer;
        long sum = 0;
        
        for(int i = 1; i <= count; i++){
            sum += price * i;
        }
        
        if(sum - money > 0) answer = sum - (long)money;
        else return 0;
        
        return answer;
    }
}