코드업(CodeUp) 2016 : 천단위 구분기호

import java.util.Scanner;

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

        int cnt = sc.nextInt();
        String n = sc.next();

        String rs = "";

        int j = 0;
        for(int i = n.length() - 1; i >= 0; i--) {
            if(j % 3 == 0 && j != 0) {
                rs = "," + rs;
            }
            rs = n.charAt(i) + rs;
            j++;
        }

        System.out.println(rs);
    }
}