그분님아

public static String getRegularNum(int input) {

char a[] = String.valueOf(input).toCharArray();

StringBuilder sb = new StringBuilder();

for (int i = 0; i < a.length; i++) {

if (i % 3 == 0 && i != 0) {

sb.append(",");

}

sb.append(a[a.length - 1 - i]);

}

return sb.reverse().toString();

}