[UPSC CSE 2013] Statistical Physics (Q291, 10M)

$N$ particles obeying Classical Statistics are distributed among three states having energies $\varepsilon_1 = 0$ , $\varepsilon_2 = k_{\mathrm B}T$ and $\varepsilon_3 = 2k_{\mathrm B}T$ , where $k_{\mathrm B}$ is Boltzmann constant. If the total equilibrium energy of the system is $1000k_{\mathrm B}T$ , calculate the value of $N$ .