For a finite group
$G$, define
$l(G)=(\prod _{g\in G}o(g))^{1/|G|}/|G|$, where
$o(g)$ denotes the order of
$g\in G$. We prove that if
$l(G)>l(A_{5}),l(G)>l(A_{4}),l(G)>l(S_{3}),l(G)>l(Q_{8})$ or
$l(G)>l(C_{2}\times C_{2})$, then
$G$ is solvable, supersolvable, nilpotent, abelian or cyclic, respectively.