title: Fastest way to find sum of digits on big numbers
body: <p>I have some big numbers (again) and i need to find if the sum of the digits is an even number. 
  I tried this: finding the sum of the digits with a while loop and then checking if that sum % 2 equals 0 and it's working but it's too slow for big numbers, because i am given intervals of numbers and if the input is 1999999 19999999999 then my program fails, i cannot complete within the time limit which is 0,1 sec. </p>
  
  <p>What to do ? Is there any other faster way to do this ? </p>
  
  <p>EDIT: The input 1999999 19999999999 means it will start with 1999999 and check all the numbers like i wrote above until 19999999999, and because we are talking about big numbers (&lt; 2^30) my program is not worthy. </p>