求一解：当输入框失去焦点后自动计算三个输入框的和，显示在第四个输入框里！

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
</HEAD>
<BODY>
<input type="text" name="num1" value="0" onkeyup="JavaScript:checkValue(this)" onblur="JavaScript:calculateTotal()">
    <br>
    <input type="text" name="num2" value="0" onkeyup="JavaScript:checkValue(this)" onblur="JavaScript:calculateTotal()">
    <br>
    <input type="text" name="num3" value="0" onkeyup="JavaScript:checkValue(this)" onblur="JavaScript:calculateTotal()">
    <br>
    <input type="text" name="result" value="0" onkeyup="JavaScript:checkValue(this)" onfocus="JavaScript:calculateTotal()"><SCRIPT LANGUAGE="JScript">
function checkValue(o) {
o.value=o.value.replace(/\D/g,'');
}
function calculateTotal() {
var intN1,intN2,intN3,intResult;
intN1=parseIntValue("num1");
intN2=parseIntValue("num2");
intN3=parseIntValue("num3");
intResult=intN1+intN2+intN3;
document.getElementById("result").value=intResult.toString();
}
function parseIntValue(o) {
return parseInt(document.getElementById(o).value);
}
</SCRIPT>
</BODY>
</HTML>