<script type="text/javascript">
function f(val) {
if (val==parseFloat(val) || val=="") { document.a.b.value=val*10; }
else { document.a.b.value="molq vuvedete 4islo"; }
}
</script>
<form name="a" action="#">
<input type="text" onkeyup="f(this.value)" />
<input type="text" name="b" />
</form>