숫자 천단위 마다 콤마 붙이기

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        StringBuilder sb = new StringBuilder();

        int length = sc.nextInt();
        int n = sc.nextInt();
        String num = Integer.toString(n);
        String[] numArr = new String[length];

        int count = 1;
        for(int i = length - 1; i >= 0; i --) {
            if(count%3 == 0 && length > 3 && i != 0) {
                numArr[i] = "," + String.valueOf(num.charAt(i));
            } else {
                numArr[i] = String.valueOf(num.charAt(i));
            }
            count++;
        }

        for(String str : numArr) {
            sb.append(str);
        }

        System.out.println(sb);

    }
}