function valid(field) 
{ 
var sk = field.value.length-1;
var re = /^[!"#$%&'()*+/:;<=>?@\[\\\]`{|}^~]*$/; 
if (re.test(field.value[sk])) {
alert('Naudojamas netinkamas simbolis!'); 
field.value = field.value.replace(field.value[sk],"");
return false; 
			      }
}