function check_input(){
    var f = document.contact_us;
    var txt_email = "Please insert your e-mail";
    var regexpemail = /^([a-zA-Z0-9_.-])+@(([a-zA-Z0-9-])+.)+([a-zA-Z0-9]{2,4})+$/;

    if(f.name.value == ""){
        alert("Please insert your name");
        f.name.focus();
        return false;
    }

    if(!regexpemail.exec(f.email.value)){
        alert(txt_email);
        f.email.focus();
        return false;
    }

    if(f.message.value==""){
        alert("Please type your message");
        f.message.focus();
        return false;
    }

    return true;
}