改改js，急！

[ubb]<script language="javascript">
var m;
function txt_changed()
{   
    var m_new;
    if(typeof(m) == "undefined")
    {
        m = $("m").innerText;
    }
    
    m_new = m;
    
    if($("averageFoodStuff").value != "")
    {
        m_new = m_new - $("averageFoodStuff").value;
    }
    
    if($("averageCrystal").value != "")
    {
        m_new = m_new - $("averageCrystal").value;
    }
    
    if($("averageMatal").value != "")
    {
        m_new = m_new - $("averageMatal").value;
    }
    
    $("m").innerText = m_new;}function $(id)
{
    return document.getElementById(id);
}
function check()
{
var n;
var l;
var food;
var ctal;
var matal;
if(document.tradeSilverAverageForm.averageFoodStuff.value==0&&document.tradeSilverAverageForm.averageCrystal.value==0&&document.tradeSilverAverageForm.averageMatal.value==0){$("btn").disabled = "disabled";}
else if ( $("m").innerText != '0' )
{
                              n = $("m").innerText % 3;
                              l = Math.floor($("m").innerText / 3);
            food = parseInt( $( 'averageFoodStuff' ).value )+n+l;
    ctal = parseInt( $( 'averageCrystal' ).value ) + l;
            matal= parseInt( $( 'averageMatal' ).value ) + l;
document.tradeSilverAverageForm.averageFoodStuff.value=food;
document.tradeSilverAverageForm.averageCrystal.value=ctal;
document.tradeSilverAverageForm.averageMatal.value=matal;
charAT(food);
charAT(ctal);
charAT(matal);
}
else ( $("m").innerText == '0' )
{$("btn").disabled = false;$("obj_div").style.display = 'block';}document.tradeSilverAverageForm.submit();
}
</script>
<form name="tradeSilverAverageForm" method="post" action="/Project/tradeSilverAverage.do"> 
输入框1： <input type="text" id="averageFoodStuff" name="averageFoodStuff" onblur="javascript:txt_changed()" value="0" size="2"> 
输入框2： <input type="text" id="averageCrystal" name="averageCrystal" onblur="javascript:txt_changed()" value="0" size="2" > 
输入框3： <input type="text" id="averageMatal" name="averageMatal" onblur="javascript:txt_changed()" value="0" size="2"> 
总值： <span id="m"> 2008 </span>
<input type="submit" id="btn" value="按钮">
</form> 
总值的余数：<span id="n"></span><br />
总值的模：<span id="l"></span><br />
<div id='obj_div' style='display:none;'>结果</div>
</body>
</html>[/ubb]
我想实现当if ( $("m").innerText != '0' )执行这个条件的时候，点击按钮，第一次点击按钮不提交，第二次点击按钮才提交，帮我看看把