title: Joining a string in another string
body: <p>I have done this code but the output is not like what I want</p>
  
  <pre><code>def replace(s,p,n):
      return "".join("{}".format(p) if not i % n else char for i, char in enumerate(s,1))
  
  print(replace("university","-",3))
  </code></pre>
  
  <p>the output that I get is <code>un-ve-si-y</code></p>
  
  <p>I must get it like :
  <code>uni-ver-sit-y</code></p>