$prefixSize = 4;   
for ($i = $this->incrementsOffset; $i < $this->incrementsMaxLimit; $i++) {
               $nextIncrementRevProposal = sprintf('%-0' . $prefixSize . 's', $i);
                if (!isset($this->busyLogins[$nextIncrementRevProposal])) {
                    $this->loginProposal = $nextIncrementRevProposal;
                    break;
                }
            }