class Solution {

    /**
     * @param Integer $num
     * @return Integer
     */
    function addDigits($num) {
    $sum = $num;
    while ($num >= 10) {
        $sum = 0;
        while ($num > 0) {
        $sum += ($num % 10);
        $num = floor($num / 10);
        }
        $num = $sum;
    }

    return $sum;
    }
}