Find The Cubical in 3d Matrix of m*n*o Efficiently !!!!

Given a 3D matrix of m*n*o dimension and there lies a cubicle in each cell of the matrix. Assume K cubicle are occupied(you know the coordinates of occupied cubicles) and remaining are vacant. You have to arrange a meeting. So find a cubicle such that the sum of the distances traveled by all the persons should be minimum. A Person can't move diagonally, they can only parallel to axes...