Parent Catogary

Add one of these in function.php
/*************************/
function get_top_parent($cat){
$curr_cat = get_category_parents($cat, false, '/' ,true);
$curr_cat = explode('/',$curr_cat);
$idObj = get_category_by_slug($curr_cat[0]);
echo  $id = $idObj->term_id;
}

/**********************/
function get_top_parent_category($cat_ID)
{
$cat = get_category( $cat_ID );
$new_cat_id = $cat->category_parent;

if($new_cat_id != "0")
{
return (get_top_parent_category($new_cat_id));
}
return $cat_ID;
}