Menu deroulant interactif

<html>
<head>
<script language="JavaScript">
function calc() {
document.f.res.value = document.f.v1.value*document.f.v2.value*document.f.v3.value;
}
</script> 
</head>
<body>
<form name="f"> 
<select name='v1' onchange="calc()"> 
<option value="0"><font face="Verdana">Choisir</font></option>
<option value="1.5"><font face="Verdana">privé</font></option>
<option value="3"><font face="Verdana">Public</font></option>
</select>
<select name='v2' onchange="calc()"> 
<option value="0"><font face="Verdana">Choisir</font></option>
<option value="1"><font face="Verdana">1 mois</font></option>
<option value="3"><font face="Verdana">3 mois</font></option>
<option value="6"><font face="Verdana">6 mois</font></option>
<option value="9.6"><font face="Verdana">12 mois</font></option>
</select>
<select name='v3' onchange="calc()"> 
<option value="0"><font face="Verdana">joueurs</font></option>
<option value="10"><font face="Verdana">10</font></option>
<option value="12"><font face="Verdana">12</font></option>
<option value="14"><font face="Verdana">14</font></option>
<option value="16"><font face="Verdana">16</font></option>
</select>
<input type="text" value="0" name="res">
</form>
</body>
</html>