function check() {
var letters = document.OrderForm.cardnumber.value.length +1;
if (letters <= 4) { document.OrderForm.cardnumber.focus()}
else {document.OrderForm.cardnumber2.focus()}
}

function check2() {
var letters2 = document.OrderForm.cardnumber2.value.length +1;
if (letters2 <= 4) { document.OrderForm.cardnumber2.focus() }
else { document.OrderForm.cardnumber3.focus() }
}

function check3() {
var letters3 = document.OrderForm.cardnumber3.value.length +1;
if (letters3 <= 4) { document.OrderForm.cardnumber3.focus() }
else { document.OrderForm.cardnumber4.focus() }
}

function check4() {
var letters4 = document.OrderForm.cardnumber4.value.length +1;
if (letters4 <= 4) { document.OrderForm.cardnumber4.focus() }
else { document.OrderForm.CardExpMonth.focus() }
}