function isNumberKey(evt)
      {
         var charCode = (evt.which) ? evt.which : event.keyCode
         if (charCode > 31 && (charCode < 48 || charCode > 57))
            return false;

         return true;
      }
function cs()
{
var n = document.form1.n.value;
if(n=="")
{
alert("please enter value ");
}
else
{
var b=(n*n);
var c=(eval(n)+1);
var f=(c*c);
var e =document.form1.e.value;
document.form1.e.value=((b*f)/4);
}
}