title: big oh of algorithm with nested loop
body: <p>find the big oh characterization</p>
  
  <pre><code>input: n  
  
  s&lt;-0  
  for i&lt;-1 to n^2 do  
    for j&lt;-1 to i do  
      s&lt;-s+i
  </code></pre>
  
  <p>Both loops iterate <code>n^2</code> times. I'm not sure if I should add or multiply the loops. Right now I think the answer is <code>O(n^4)</code>.</p>