if one input of two are not empty

How can i make an "if" condition that is mean if one input of two are not empty then cann go further.

I make a condition

if(empty($username)||empty($email)|| empty($f_name) ||empty($l_name) || empty($password) || empty($repassword) || empty($mobile)
|| empty($iban) ||empty($bic) || empty($kartennumer) || empty($cvv) {
    echo "
        <div class='alert alert-warning'>
            <a href='#' class='close' data-dismiss='alert' aria-label='close'>&times;</a><b>Bitte geben Sie alle Felder ein...!</b>
        </div>
    ";
    exit();

}

But I want to make if $iban and $bic are complete than I don't need to complete $kartennumer and $cvv. How can I make that ? I try more solution and I can't finde it?