The disproportionation of $\mathrm{MnO}_{4}^{2-}$ in acidic medium resulted in the formation of two manganese compounds $\mathrm{A}$ and $\mathrm{B}$. If the oxidation state of $\mathrm{Mn}$ in $\mathrm{B}$ is smaller than that of A, then the spin-only magnetic moment $(\mu)$ value of B in BM is __________. (Nearest integer)