PREFIX : <http://example/>
PREFIX  n: <http://example/x#> 
PREFIX  rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX  rdfs:   <http://www.w3.org/2000/01/rdf-schema#>
PREFIX  xsd:    <http://www.w3.org/2001/XMLSchema#>

SELECT (count(*) as ?c)
{ 
    ?x n:p* ?z .
    ?x n:p ?z .
}