  Deterministic extraction of Bell pairs from a finite number of partially
entangled pairs is discussed. We derive the maximum number of Bell pairs that
can be obtained with probability 1 by local operations and classical
communication. It is proved that the optimal deterministic concentration needs
only a two-pair collective manipulation in each step, and that a collective
manipulation of all entangled pairs is not necessary. Finally, this scheme
reveals an entanglement measure for the deterministic concentration.
