A system consisting of three Ising spins in a line is coupled by nearest Neighbour interactions. S(1) S(2) S(3) The system is placed in an external magnetic field B in the z-direction and is in thermal equilibrium at temperature T. If each spin has magnetic moment m and the Hamiltonian for the system is given by H = JS,(i)S (i+1) HS, (1) where J and m are positive constants. If the Sz(i) can take value either +1 or -1, the difference between maximum and minimum value of energy of the system is