php - generate a 4 digit number

For the captcha, the code below generates a 5-digit number. I want it to be 4 digits. how can I do it.

// generate random numbers
$sayilar = '';
for ($x = 15; $x <= 95; $x += 20) {
    $sayilar .= ($sayi = rand(0, 9));
    imagechar($image, rand(3, 5), $x, rand(2, 14), $sayi, $textcolor);
}