Count all interactions from BioPax datasets (SPARQL 1.1)

Database: 
Statement: 
All interactions from BioPAX dataset.
A limit of results per page $number$ (e.g., 10)
Query: 
PREFIX biopax-2: <http://www.biopax.org/release/biopax-level2.owl#> SELECT (COUNT(?s) AS ?cnt) WHERE { ?s a biopax-2:interaction } limit ??number