a = 3, b = 5 이면 3 + 4 + 5 = 12 출력class Solution {
public long solution(int a, int b) {
long answer = 0;
int start = Math.min(a, b);
int end = Math.max(a, b);
for(int i = start; i <= end; i++) {
answer += i;
}
return answer;
}
}