A combinatorial formula for monomials in Kontsevich's $\psi$-classes

Diagonal complexes provide a simplicial model for the Kontsevich's tautological bundles over $\mathcal{M}_{g,n}$. Local combinatorial formula for the first Chern class yields a combinatorial formula for the $\psi$-classes (that is, first Chern classes of the tautological bundles). In the present paper we derive a formula for arbitrary monomials in $\psi$-classes.