title: how to calculate reverse modulus
body: <p>now I have one formula:</p>
  
  <pre><code>int a = 53, x = 53, length = 62, result;
  result = (a + x) % length;
  </code></pre>
  
  <p>but how to calculate reverse modulus to get the smallest "x" if I known result already</p>
  
  <pre><code>(53 + x) % 62 = 44
  //how to get x
  </code></pre>
  
  <p>i mean what's the formula or logic to get x</p>