title: How to produce numbers in some step bounds?
body: <p>I want to produce numbers with some steps,
  for example for step 4, i want to produce:</p>
  
  <pre><code>1   -&gt; 0
  3   -&gt; 4
  4.1 -&gt; 4
  15  -&gt; 16
  etc.
  </code></pre>
  
  <p>for step 0.2:</p>
  
  <pre><code>1     -&gt; 1
  3     -&gt; 3
  4.1   -&gt; 4.2
  15.99 -&gt; 16
  etc.
  </code></pre>
  
  <p>Do you know nice formula to produce numbers like these?</p>