The compound shown is 1,2-dimethylcyclopropane drawn without stereochemistry. Treat the ring as planar and count configurational isomers only. How many stereoisomers does it have? Give an integer.

C1 and C2 are both stereocentres. The cis isomer has both methyls on the same face; it has a mirror plane through C3 and the midpoint of C1-C2, so it is a single meso compound. The trans isomer has the methyls on opposite faces, no mirror plane, and exists as a pair of enantiomers $(1R,2R)$ and $(1S,2S)$. Total: $1+2=3$.