public static int beautifulDays(int i, int j, int k) { if (i < 1 || j < 1 || k < 1) return -1;

int count = 0;

for (int n = i; n <= j; n++) {
    String wordInt = String.valueOf(n);
    int x = 0;
    int y = wordInt.length() - 1;

    while (x < y) {

        char chFront = wordInt.charAt(x);
        char chLast = wordInt.charAt(y);


        wordInt = wordInt.substring(0, x) + chLast + wordInt.substring(x + 1, y) + chFront + wordInt.substring(y + 1);

        x++;
        y--;
    }

    int num = Integer.parseInt(wordInt);
    int difference = Math.abs(num - n);

    if (difference % k == 0) {
        count++;
    }
}
return count;
}