  We generalize the small cancellation theory over hyperbolic groups developed
by Olshanskii to the case of relatively hyperbolic groups. This allows us to
construct infinite finitely generated groups with exactly $n$ conjugacy classes
for every $n\ge 2$. In particular, we give the affirmative answer to the
well--known question of the existence of a finitely generated group $G$ other
than $\mathbb Z/2\mathbb Z$ such that all nontrivial elements of $G$ are
conjugate.
