Extra number in header/top row of HTseq count matrix output

My count matrices all have an extra number in the header or top row, does anyone know why this is and if I can just delete it? (example pic attached)

The number doesn’t seem to correlate to a sample or job number (it is sometimes 0) and is different in each output (I’m batch running HTseq). It also doesn’t seem to be a matter of the columns not lining up as there are no extra or missing numbers at the tail end of the output