title: How can I do this effectively?
body: <p>This problem:</p>
  
  <p>Input: 123456</p>
  
  <p>Result:</p>
  
  <pre><code>1+2+3+4+5+6 = 21
  2+1 = 3
  </code></pre>
  
  <p>Return: 3</p>
  
  <p>This is my code:</p>
  
  <pre><code>num = input()
  print(sum(list(map(int, list(num)))))
  </code></pre>
  
  <p>I don't know how to do until it is 1 digit.</p>