code: def _n_slices(trajectory, max_slice_length, margin):
      """How many slices of length upto max_slice_length in a trajectory."""
      # TODO(lukaszkaiser): add option to sample from n last trajectories.
      if not max_slice_length:
          return 1
      # A trajectory [a, b, c, end_state] will have 2 slices of length 2:
      # the slice [a, b] and the one [b, c], with margin=0; 3 with margin=1.
      return max(1, len(trajectory) + margin - max_slice_length)
  
imports: import collections
  import os
  import gin
  import gym
  import numpy
  from trax import fastmath
  from trax.rl import advantages
  from trax.supervised import training
label_desc: Use image node_id 5 for calling a global function with example usage: _n_slices(trajectory, max_slice_length, margin) and returns: max, int