function check_email(email) {
    b = true;
    if (email.lastIndexOf('@') < 1)
        b = false;
    if (email.lastIndexOf('@') > email.lastIndexOf('.'))
        b = false;
    if (email.lastIndexOf('@') == email.lastIndexOf('.')+1)
        b = false;
    if (email.length-email.lastIndexOf('.') < 3 || email.length-email.lastIndexOf('.') > 5)
        b = false;
    if (email.length<6)
        b = false;
    return(b);
}