">sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">z</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">*</span><span class="n">z</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="w">               </span><span class="k">IF</span><span class="w"> </span><span class="p">(</span