[프로그래머스] 부족한 금액 계산하기

class Solution {
    public long solution(int price, int money, int count) {
        long answer = -1;
        long sum = 0;

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