title: Fibonacci sequence algorithm in Javascript
body: <p>I need to solve a Fibonacci question using JavaScript.</p>
  <p>The function should have 3 parameters: 2 initial values and a final value.</p>
  <p>The function should return the position of the final value in the Fibonacci series starting with the given initial values.</p>
  <p>For example:</p>
  <p>input: 2,5,19</p>
  <p>output: 5
  Because the series is 2,5,7,12,19 = 5</p>
  <p><strong>how?</strong></p>