The optional 10-minute check-up

A handful of problems, picked to locate a starting point on the Depth ladder. No score, no ranking, no signup — it ends with a path, not a grade. You can skip it forever: every topic on the site works without it.

Answering "not sure" is fine — it just points the search lower. No hints here on purpose: we're locating, not teaching.

Something missing from this problem? Tell us and we'll swap it — it won't count either way.

Here's a good place to start

← Or browse everything · Run it again