/**
 * Divides {@code n} by 2.
 *
 * @param n
 *            {@code NaturalNumber} to be divided
 * @updates n
 * @ensures 2 * n <= #n < 2 * (n + 1)
 */
private static void divideBy2(NaturalNumber n) {
    int lastDigit = 0;
    if (!n.isZero()) {
        lastDigit = n.divideBy10();
        if (!n.isZero()) {
            int remainder2 = n.divideBy10();
            if (remainder2 % 2 != 0) {
                lastDigit = lastDigit / 2 + 5;

            } else {
                lastDigit = lastDigit / 2;
            }

            divideBy2(n);
            n.multiplyBy10(lastDigit);

        } else {
            lastDigit = lastDigit / 2;
        }
    }
    n.multiplyBy10(lastDigit);

}