public long solution(int k, int d) {
long answer = 0;
for (long i = 0; i <= d / k; i++) {
long x = i * k;
long y = (long) Math.sqrt((double) d * d - x * x) / k;
answer += y + 1;
}
return answer;
}출처:https://school.programmers.co.kr/learn/courses/30/lessons/140107
