Thanks for answer.
Now I can get gene ids, but they are in type of Ensembl Gene ID. So I need to convert them to KEGG Gene ID.
KEGG REST API allows conversion from ncbi-gi, ncbi-geneid and uniprot. So these types are also ok for me. I can convert them using following rest url.
http://rest.kegg.jp/conv/genes/ncbi-geneid:3113320
Do you know a way to convert from ENSG to other ids?