s</span><span class="p">(</span><span class="n">bonds</span><span class="p">)</span>
                    <span class="k">for</span> <span class="n">_</span> <span class="ow">in</span> <span class="n">slabs</span><span class="p">:</span>
                        <span class="n">num_surfaces</span> <span class="o">+=</span> <span class="mi">1</span>

    <span class="k">return</span> <span class="mi">3</span> <span class="o">-</span> <span class="nb">min</span><span class="p">(</span><span class="n">num_surfac