Filter BAM dataset on spliced alignments

I’m trying to filter reads with skipped regions/spliced alignments which have N bases in the cigar string. I’m using the following tool: Filter BAM datasets on a variety of attributes (Galaxy Version 2.5.1+galaxy0). I selected the option to filter on cigar string but do not know how to give a command to filter only reads with the ‘N’ base. Does anyone know how to do this?