The Hamiltonian of a system of \( N \) particles in volume \( V \) at temperature \( T \) is \( H = \sum_{i=1}^{2N} a_i q_i^2 + \sum_{i=1}^{2N} b_i p_i^2 \) where \( a_i \) and \( b_i \) are positive constants. The ensemble average of the Hamiltonian is \( aNk_B T \), where \( k_B \) is the Boltzmann constant. The value of \( a \) is _____ (in integer).