Turán number of three disjoint cliques of arbitrary sizes

The Turán number $\rm ex(n,H)$ of a given graph $H$ is the maximum number of edges in an $n$-vertex $H$-free graph. In this paper, for all $p\ge q\ge r\ge 2$ and $n\geq p+q+r$, we determine the exact value of $\rm ex(n,K_p\cup K_q\cup K_r)$ and describe all extremal graphs.