/**
 * nth element in the fibonacci series.
 * @param n >= 0
 * @return the nth element, >= 0.
 */
function fib(n) {
  var a = 1, b = 1;
  var tmp;
  while (--n >= 0) {
    tmp = a;
    a += b;
    b = tmp;
  }
  return a;
}

document.write(fib(10));