Is it worth doing 4 A-levels or focusing on 3?

I'm doing exactly those a levels (le français est ma langue maternelle aussi) and am enjoying them a lot. I'd say try it out because you can always drop French if it's too much. French is not benefitting my university applications though, as doing four A levels doesn't have any advantage for admissions. That said, some sixth forms will not let you take three A levels if one of them is further maths (this is the case at my school, you can only drop another subject if you do well enough at AS). It's often said that this is because unis don't treat maths and further maths as full separate A levels, but I haven't seen any universities actually say this. I believe the main reason is simply because the dropout rate for further maths is so high - there were 20 of us at the start of year 12 and now there are only nine