title: How to return the time, which would take for a method to finish it's job?
body: <p>I have a simple recursive algorithm, which returns Fibonacci numbers:</p>
  
  <pre><code>private static double fib_recursive(int n){
      if(n &lt;= 2) return 1;
      else return fib_recursive(n-1) + fib_recursive(n-2);
  }
  </code></pre>
  
  <p>Now my task is to return the time, which this method <strong>would</strong> take to calculate the <strong>400-th</strong> fibonacci number on a given computer e.g. fib_recursive(400). "Would" is in bold, because I can't run the function, as it would take to long for this method to give an answer.</p>
  
  <p>How can it be best achieved?</p>